First off, do you mean "narcrosis" or "necrosis".......big difference! The first one means the bowel in question has kind of spazed out due to use of opioid meds. The latter means the bowel literally died and was removed before the rest of it died as well. If it's the first one, I would guess the tests would be to see if the narcosis has reversed completely, and the part of the rectum that's left is intact and back to its old self. If it's the latter, then they need to know what's left is functionally still alive and not dead like what they removed. They'd also need to know why the necrosis happened in the first place. Otherwise, reconnecting could allow the necrosis to continue........in which case you'd really be screwed. Sorry to be so blunt. But reconnection can only be successful if blood flow through the connection occurs. And if one end is dead (narcrosis), connecting to it will cause your healthy connected bowel to die as well.
If I were you, I'd get multiple opinions on the subject of reconnecting before going through all that. And don't just focus on the advice for the outcome you want........always consider how bad it could be if things don't work out as planned. You don't want the optimistic version of the outcome........you want the most likely. Very interested to hear what they say......and of course, best of luck to you!!!
Regards,
Bob