I could see the term Squib sticking, or at least, perhaps another variation of the word, but ultimately with the same meaning. You can introduce political correctness in everyday language, but it's the more ingrained ideas that are harder to shift. Being a Squib is considered something almost shameful - Filch, for example, is horrified that Harry may have seen his KwikSpell letter - but it's held in far higher esteem than being simply a mere Muggle. Arabella Figg lives in Privet Drive, but she still remains connected to the magical world. It's not a tie that many people would be willing to give up, I imagine. While ultimately being a Squib is in fact no better than being a Muggle (I'd even consider it to be worse, living and growing up in a world you could never truly belong to or be accepted by) it still traces back to that supremacist 'Magic is Might' belief. I think Squibs would endeavour to make that distinction, regardless of new terminology regarding political correctness.