I can see an agreement between club and player pre-Rangnick. Yes, quite possible as the player must have been extremely frustrated.
What I don't see is how he left the door without RR assessing him and making a decision on it. I don't see any manager at this level of football not having the gumption and initiative to come in and say "hang on this guy's going to be a top player for me, why's he got an informal agreement going to a relegation side?"
The idea he could simply accept that is unfathomable to me, and then the idea you wouldn't play him over X amount of important games just because he's got a loan lined up is weird, you're talking as if it's a 50 million transfer. The player could get injured now or at Everton, that's football, there is nothing particularly important to the club contingent on him not getting injured, it's just a loan. The games are way more important and they also form part of an opportunity to convince the player to stay if RR wanted him so that also makes no sense.
Just doesn't add up at all, I think RR came in, assessed him, came to whatever reasoning he did and said he can go on loan in January. Doesn't require all these totally weird lines of reasoning that are so wishy washy that I'd be really disappointed in Ralf.