INEOS will fire ETH definitely, there is no scenario where he keeps his job, it's just about when that will be. This isn't the last year of his contract, he still has time, so it's clear that he expects to manage the team next season. But I am writing right here, I guarantee you that ETH will not manage the team next season. Either he will be fired soon if the team gets worse and worse, or he is going to be fired at the end of the season.
The only possible way that he doesn't get fired, would be getting some wins to keep the team going up in standings, and then win something, sure they won't win the premier league, but what if they win Europa this season? They started terrible but that doesn't mean they won't win it, there is a possibility that they could. If something like that happens then maybe he will stay. But I am sure that they will have a season where they win absolutely nothing, and if he keeps getting worse then I am sure he won't even see the end of the season neither.
It's quite funny but United were recently the favourites for the Europa League, now the bookmakers have adjusted their opinion and Tottenham are the favourites with 5.0 odds. However, United are still listed as the second contender with 6.70 odds. But in my personal opinion, even if you double the odds, a bet on United won't be profitable until Ten Hag is sacked. Besides Tottenham there is Roma, Sociedad, Athletic, Lazio and United can't even beat Twente.
As for the sacking, in my opinion it is a matter of a few rounds, there is too much noise around already - even indifferent fans of other clubs are surprised how United could fall so low. The sacking has been justified for a long time, but now it already looks like an image necessity.