Baba Basra 153a - Shechiv Mei'ra: If he is healed is it an automatic retraction of the gift?

The gemara said many times that one who gives a mat'nas shechiv meira (either gives all their possessions or they mention that they are dying at the time of the gift), if they are "a'mad" and recover from their illness that can retract the gift. Is the retraction automatic, or must they explicitly retract?

Tosafos is bothered about the dispute in the gemara between the receiver of the gift and the inheritors, whether it was a matnas shechiv mei'rah which allows for retraction, or a matnas ba'ri that is fully binding. Even if the inheritors claim is correct that it was a matnas shechiv meira that allows for retraction, and even if he actually recovered from his original illness, who said that he retracted from the gift before dying? Tosafos explains that אם עמד חוזר means that as long as he recovers we assume that he retracted, even though we have no evidence that he actually retracted. In analyzing Tosafos, they aren't saying that recovering is a chazara, rather that when we don't know whether he actually retracted or not, we make an assumption that if he recovered that he retracted. If we would somehow know for sure that even though he recovered, he definitely didn't retract, the matana would be binding.

However, the Rambam (Hil. Zechiya 8:14) seems to hold that when he recovers the matana is automatically void because it was only meant to be given after he died:

שאומדן דעת הוא שלא נתן זה הכל אלא ונתכוון שלא יקנו כלום אלא לאחר מותו

The Rambam holds that the default is that the matana is not binding until he dies. The language of אם עמד חוזר isn't accurate because the default is that until he dies there is no gift at all. The gift only goes into effect when he dies. The Shulchan Aruch (C.M. 250:2) writes explicitly that the gift is automatically void - אם עמד ונתרפא לגמרי המתנה בטלה ממילא, by adding the word "me'meila" it implies clearly that he doesn't need to actually retract. This is very different from Tosafos who assumes that the default is that the gift is binding, just that he has the right to retract if he recovers. The GR"A (5) seems to point out that Tosafos doesn't agree with the Shulchan Aruch.

The Nesivos (250:2) raises a chakira whether a shechiv mei'rah who is still sick maintains the right to retract. Although the ketzos assumes that he isn't able to retract, the Nesivos points to the sm"a who indicates that even in his illness he has the right to retract. This should be dependent on the machlokes Rambam and Tosafos. If we assume that the matana is binding but he has a right to retract if he recovers, then until he recovers he doesn't have that right. But, if the gift was only meant to be binding at the time of his death (Rambam), until then he can retract even if he doesn't recover from the illness.

The Rashbam 146b seems to have a third approach. The Rashbam writes:

שנראין הדברים שמחמת מיתה נתן ועל מנת שאם לא ימות לא יתקיים המתנה

This implies that we view it as a gift that is given immediately but their is a condition that it is only effective if he dies. Therefore, the Rashbam will agree with the Rambam that if he recovers he doesn't actually have to retract, it happens automatically because the condition wasn't fulfilled. But, so long as he is still ill, the rashbam would agree with Tosafos that he doesn't have the right to retract.