I would disagree with what you've heard. There is no reason not to use that yeast again, and I certainly don't think it will have mutated. One concern could be that over several batches the yeast will get stressed. But you should be able to do 4 or 5 generations. Most commercial brewers do this with high gravity beers. If you have a 9% beer than alcohol can sort of stun or kill the yeast, but I still wouldn't worry much about it.
Ideally you should just try to brew something similar, with hop flavour. But even still, you won't ruin a batch unless it's infected.
1.060-5 isn't really that high. If this was true half the guys on here couldn't repitch, because most of them are make 1.060 beers at minimum!
In Process - Russian Imperial Stout, Nelson Sauvin Rye IPA, Mild No.3
In Kegs - Barley Wine, Apfelwein, Wild BlackBerry Wheat, Coffee Oatmeal Porter
Gone - so many :(