That would be very dangerous and possibly the plot of some hard sci-fi thriller. If immortal mice were to somehow escape the lab and breed in the wild we could rapidly end up with massive populations of mice that never die of aging, ultimately collapsing entire ecosystems and food chains, leading to the end of humanity.
2. The most common causes of death for wild mice are predation, diseases, and starvation. Theoretically immortal mice have no chance in the real world if not very well-adapted to these conditions.
It’s also not hard to imagine that an immortal organism has higher metabolic needs. Meaning they are more prone to starvation and potentially less fit.
It's my understanding that mice don't live long, because slower aging didn't provide a significant evolutionary advantage (lot's of predators, mainly). Instead the rate of reproduction settled at a very high level [1]. So by that logic, engineered, non-aging mice wouldn't have much of an advantage in the wild.
