Ehlers has outscored Necas at even strength over the last three seasons, despite playing about 78% of Necas' minutes. He isn't even capable of replacing Nik's actual point production, and then he'd also be tasked with playing C (which he cannot do) and carrying the rest of the line on his back. Considering that we already have a losing first line, it kind of doesn't sound like a recipe for success.
Unfortunately, this reeks of the Trouba situation. A lot of posters hated his guts for wanting to leave, which is understandable enough, but the fact that those posters also claimed that he was replaceable was nonsense. Yes, our hands were forced, but we still don't have a replacement, nor are we anywhere close to having one in the system. The same goes for Ehlers: we have nothing to replace him with, we cannot get anything close to him in a trade, and none of the prospects are good enough to take on his responsibilities. If Ehlers just wants out, then there's little we can do, but if this is about us lowballing him, maybe it'd be time to accept the reality and pay the guy.