Gemara

51a (Mishnah): If she gets sick, he must heal her. He may say 'I divorce her. here is a Get and her Kesuvah, let her heal herself.'

(Beraisa): A widow is fed from the orphans. Medical expenses are like food;

R. Shimon ben Gamliel says, medical expenses with a limit are taken from her Kesuvah. If there is no limit, they are like food.

(R. Yochanan): In Eretz Yisrael, bloodletting is considered to be unlimited.

R. Yochanan's relatives lost their father; the widow had daily medical expenses. He advised them to get a doctor to fix a price to treat her permanently (so it will be deducted from the Kesuvah).

R. Yochanan: I acted like a lawyer (which is wrong - Avos 1:8).

Question: Why did he initially advise them, and later regret it?

Answer: Initially, he thought that he should fulfill "Do not hide from your flesh (kin)". Later, he thought that an important person should not do so (his counsel hurt the widow).

Rishonim

The Rif and Rosh (4:23) bring our Gemara, and rule like R. Shimon ben Gamliel.

Ran (DH Gemara): The Halachah follows Shimon ben Gamliel because R. Yochanan holds like him.

Ran (DH Masnisin): He can say 'here is a Get and her Kesuvah, let her heal herself' because one need not feed (or heal) his exwife.

Rosh: In Eretz Yisrael they used to let blood regularly, so it is unlimited, like food. Cures of limited cost are like redemption. Heirs are exempt from this, just like they need not redeem her. Seemingly, in her husband's lifetime there is no difference whether or not there is a limit. However, the Yerushalmi says 'if it is fixed, she pays. If not, her husband.' However, it is better to say that the Yerushalmi was succint and omitted words to avoid making an argument with the Bavli.

Ran (DH Gemara): The Mishnah says Stam that her husband must heal her, i.e. even if it is unlimited. The Ba'al ha'Itur proves from the Yerushalmi that also a husband is exempt in this case. It seems that the Yerushalmi discusses a widow, and it means '...if not, the property of her husband'. When her husband is alive, the Rambam does not distinguish (between limited and unlimited).

Rambam (Hilchos Ishus 14:17): If she gets sick, he must heal her until she is healthy. If he saw that it is an extended ilness and he will lose much money healing her, and told her 'here is your Kesuvah. Heal yourself from it, or I divorce you', we heed him. It is improper to do so.

Magid Mishneh: The Ra'avad says that the Sifri learns from "V'Shilachtah l'Nafshah" that one may not divorce a Yafes To'ar until she is well. All the more so one may not divorce a Bas Yisrael until she is well! Our Mishnah is when she is not bedridden. It seems that the Rambam disagrees, for the Mishnah or Gemara should have said so. Yafes To'ar is a Chidush. The Torah permitted her for a concession to the Yetzer Ra, and had compassion on her for she is a captive in a land foreign to her. Her captor had Bi'ah with her b'Al Korchah (against her will) and she has no way to heal herself. Therefore, he cannot send her until she can walk. Perhaps it is an Asmachta mid'Rabanan.

Rebuttal (Kesef Mishneh): The Sifri itself makes the Kal va'Chomer to Benos Yisrael! It seems that the Rambam understands that the Sifri is like R. Yonason, who says that the verse discusses divorcing her with a Get after Kidushin. The Rambam rules like Chachamim, who say that it discusses sending her away before there was Kidushin, so surely we do not expound an obligation to wait until she is well. In any case we learn that it is improper to expel a wife before she is well.

Rambam (18:5): If a widow became sick, if the cost of the cure is unlimited, it is like food, and the orphans must heal her. If it is limited she is cured from her Kesuvah.

Poskim

Shulchan Aruch (EH 79:1): If she gets sick, he must heal her whether or not the cost is limited. A widow is healed from his property only an unlimited cure, which is like food.

Taz (1): Since it is like food, orphans are obligated to cure her only as long as they are obligated to feed her. If her husband told her to keep her earnings and feed herself, he is exempt from an unlimited Refu'ah.

Shulchan Aruch (3): If he saw that it is an extended ilness and he will lose much money healing her, and told her 'here is your Kesuvah. Heal yourself from it, or I divorce you', we heed him. It is improper to do so.

Beis Yosef (DH u'Mah she'Chosav v'Im): Tosfos says that he can say so because Refu'ah is included in food, and she already received corresponding to her earnings.

Chelkas Mechokek (2): Perhaps the same applies if it is not an extended ilness, and the Shulchan Aruch just discusses a normal case.

Chelkas Mechokek (3): Nowadays that we do not divorce b'Al Korchah, one must heal her first. However, the Mizrachi says that even nowadays one may divorce b'Al Korchah if he pays her Kesuvah.

Beis Shmuel (4): Normally one may not divorce Zivug Rishon (except for immorality - EH 119:3), nevertheless the Mishnah and Poskim do not distinguish (this is allowed when she is sick). Likewise, one may divorce b'Al Korchah if she is sick.