It is clear that when a bechor has a mum that will heal by itself, it qualifies as a temporary mum. Although it cannot be sacrificed as a korban until the mum heals, it would not constitute a mum to permit the shechting of the bechor as the gemara said on 37b. Tosafos discusses a mum that will not heal on it's own, but is curable through medical intervention. According to the first approach of Tosafos any mum that is curable, even if it will take medicines or surgeries, would qualify as a temporary mum thereby retain full kedusha of bechor. According to the second approach of Tosafos, a mum that requires some form of medical intervention to heal it, would qualify as a permanent mum and the bechor my be shechted and eaten without the medical intervention.
This second approach of Tosafos opens up a very peculiar status. One can have a bechor with a mum that is curable but will not heal on it's own and is permitted to shecht it since it doesn't retain the kedusha of bechor. But if he decides to offer the medical treatment to cure the mum, the kedushas bechor will return. The Maharit Algazi questions whether this it is possible for the kedusha of a bechor to be restored through the healing of it's mum. It is very different than a temporary mum where the bechor retains it's full kedusha status even while it has a mum, just that it can't be brought as a korban. Here the kedusha status actually disappears when it gets the mum that will not heal on it's own, therefore you can shecht the animal and eat it, but if you fix the mum the original kedusha status will return.
The Maharit Algazi cites a very interesting source for this phenomenon. The gemara says in Yoma 64a learns from a pasuk that after a temporary mum heals the animal can be brought as a korban. Why would we need a source for this, can't we simply learn from bechor that after the temporary mum passes the animal becomes fit for a korban? It must be that the pasuk comes to teach us that even when the mum is a mum that won't heal on it's own so that it qualified as a permanent mum and the animal lost it's kedusha status, after the mum is healed through medications the kedusha will return.