I could definitely see that happening with Scots Gaelic in particular. There are only like 60000 speakers out there, and I'd wager a good number of them are in the latter part of their lives now. Not sure there are enough new speakers of the language in the next generation to fill that void. I think according to a census a couple of years ago, there were 3000 or 4000 fewer fluent Gaelic speakers in the country compared to back in 2000, but also a lot more young people who said they were studying it. So really it becomes a question of how many of those young learners continue with the language.
Yeah, there are going to be a lot of languages that die out completely over the next 100 or 200 years. Probably a very sizeable chunk of the world's languages when you add them up, actually. Sad, but like you say, kind of one inevitable result of the march of history. Particularly in the case of languages like Scots Gaelic where you didn't only have linguistic natural selection at play, but also a concerted effort over many years to suppress and destroy the language.