While I broadly agree with you, I'd only bet money depending on the odds the bookie is giving, and I wouldn't bet on 1:1 odds either.
The reason is because those timescales are a full generation away. Since the entire value of FB is in the social network of people, it's possible that the upcoming generations bypass FB altogether for a competitor, and FB is unable to risk the pivot[1].
[1] FB might have to intentionally discard the aging existing users for the new users if the featureset that the new users want is exclusive with the featureset that the old users want.
If they didn't think their main product would decline or get unpopular soon, why would they bet on spending $1B on buying Instagram before anyone else and copy the greatest hits and main features found in other competitors (Stories, Disappearing posts, etc) directly into Instagram first?
Without Instagram, Facebook would likely have sunk much faster and I already said they will be around for 10+ years.
So the death of Meta Platforms has been greatly exaggerated.
That day is very far into the future (in tech terms). 1.96 billion users are a whole fucking lot of a base to bleed. I would bet actual money that they won't dip below 1 billion by 2035, and that they would be still there (in whatever profitable form) with the same trademak in 2050.