If Jackson falls off it'll be because his athleticism/running ability declines significantly and/or if injuries take a toll.
I don't think there's anything schematic or philosophical that they're losing with Harbaugh that's going to hurt Jackson.
I think we've seen it a bunch this year with Jackson. He doesn't look athletically like the same guy. I don't know if it's that he wasn't fully healthy or stuff has just caught up with him. But without that he just doesn't consistently win as a passer.
Harbaugh isn't a schematic coach that's true. But he does normally have competitive teams and I think there's something to be said for that.
He's not the only good coach out there of course, so I'm not saying Baltimore can't win without him. Obviously they can. But it'll hinge on whether Jackson is the same guy anymore and to me he doesn't look like he is. The fact that they were even in position to make the playoffs in the final game is a testament to how good a coach Harbaugh is because I don't think that's a very good team outside of Henry. (Obviously it also helps that the division wasn't great this year and Pittsburgh lost to Cleveland.)