I watched the video but it was mainly hearsay, and my definition of guarantee is different to that guys. If they had guaranteed him a seat he would be signed up to a contract locking him in to a seat and wouldn't be **** off to McLaren. Clearly none of us know the wording of his contract with Alpine but at this point it seems like it was more like a promise than a contract.
The money they've spent on testing that they've used him for is largely irrelevant from my perspective, if they'd offered him an Alpine seat and a long contract he'd have taken it, he's well within his rights to leave if they haven't signed him up.
Alpine have been caught trying to hoard F1 drivers and now they have 1 left. They tried to keep Zhou on the sidelines as well this year iirc as their reserve reserve but he signed with Alfa instead.
Serves Otmar right, he's been a talking **** about Alonso all season. Alpine are a mess.