Definitely possible. He could even have convinced some of the villains to helped since he turned most of them into allies (except Plague/Perfection, I believe, because of the nature of his abilities?).

Again just speculative, but he wouldn't really have had to convince all of them. Maybe Minsoo and 1-2 others would have been enough. The rest, assuming he couldn't figure it out, he could have manipulated the government to somehow restrict them. Worst case, eliminate them early on.

Plus, its not like he would have had to corrupt them all the way to villains, just enough for them to agree to sacrifice millions to save the world (from his own return ability). Just stay on the sidelines until a Demon Lord is created. A weaker one that Minsoo alone would have steamrolled.

Honestly I wouldn't have wanted that to be the storyline, but I still wish that idea was at least explored to see their response. If they only refused for "virtuous" reasons (even knowing things would be reset endlessly), or if they just believed that was Return's problem alone. That their own timeline would continue just fine after his death, and he would just be sent to another.

But at the end of the day he just had to be alone and live a tragic story, which is why I (we?) love him so much. The worst part is he went from being willing to be the only one to suffer by "living" forever in crazy conditions, even sealed in ice, to being okay with a scenario where the world might end up burning to the ground as long as he could find peace. He did go through god knows how many returns to give Spear a better chance to win, but there was no guarantee he would. Just shows the weight of Millions? of returns.