If the UK proves itself to be a partner that doesn't want special treatment like before, it sure can be welcomed back by the EU, and if anything it coming back will only strengthen the union by showing that leaving it was considered a mistake in the end.
But I still feel skeptical regarding Brits and British politicians actually being ready to accept the fact they're not special and that they will not have special treatment. I am pretty sure they'll want to pull a sneaky and try to sneak something in to calm down the Tories.