When we embarked on our migration into AWS, we thought about this pretty carefully. There wasn't anything that we couldn't move in a year. That provides a sufficient backstop (IMO) to anything becoming untenable in the AWS ecosystem. Most everything could be moved in a handful of weeks of effort, or at least enough parts to achieve the reason to move.

AWS is still in a battle for market share; I think they're extremely "friendly" to their customers at this phase of the game. Will that change in a half-decade or decade? Maybe, but I think they're earning their profits now and likely to continue to do so.