So sorry to hear of these issues with your guy. There is a Yahoo group for dogs with LP who have the surgery, one for alternative treatments for LP, and one for ME. The ME one was quite helpful for me when I had an older IW with it. I belong to all of them as we were seeking a diagnosis, turned out mine was negative for MG and LP (there is also a complex of symptoms called GOLPP), but it can be helpful to figure out what the diagnosis actually is, as there can be some initial confusion and some overlap with these conditions.
The older labs seem prone to ME as well as LP, and they can have both, or rather, all three, including MG.
ME can often be managed with changes in diet, medication, and management. The yahoo lists are great for giving you very detailed info, resources, and support.
I feel for you!! The info I gained allowed me to keep our older hound with a good quality of life for much longer than I would have otherwise, I learned a lot. We lost her recently, almost a year after diagnosis, from unrelated causes, but I am grateful to those vets and nonvets on the lists who offered much practical advice.
I would take it one day at a time, you do not need to immediately decide whether to take this dog with you, just figure out what is best for now, and things will probably clarify themselves in time.