How long Wilder gets is entirely down to how the team plays. All the Bladey Blades (and probably some intellectual superiors) like his blunt honesty in interviews, but positive Nigel's interviews went down well until it became clear they were just meaningless soundbites that he had no clue how to back up. He didn't get sacked because he'd had the job for a year, he got sacked because he was doing a really shit job and turned a decidedly average side into a piss-poor side.
A lot of people on here last season were constantly defending Adkins, blaming the players and Clough's signings (something that still goes on now) rather than the manager being held accountable for his obvious failings, that's probably the only reason he lasted until the summer as he was already failing badly by October. Wilder's Blade status will get him some slack just the same, but if the end result is the same type of dross that Adkins was serving up then come the end of the season, Wilder will be under pressure. Try hard, but lose all the time, he might be gone by September.
Promotion isn't essential, but challenging for promotion (or at least competing to win games) is. This is a very poor division, you don't have to be a great team to make the play-offs in it, but you have to be fairly crap to aimlessly drift out of contention.
For Wilder (or any manager) to keep his job next season there has to be something to build on from this season. Clough probably should have got a few months more to try and build on what he had. Adkins had nothing to build on so got the chop. As long as Wilder is taking us forwards he'll keep his job, promotion or not.