I've seen this concerned raised a few times especially by those "against" Mourinho, using Chelsea's last season as a stick to beat him with. It's a valid concern, though to put it into perspective, that season at Chelsea was an anomaly and not the norm.
It could easily go the other way, where Mourinho finally finds a club where he can settle down at because, let's face it, it will probably be the first elite club he's at where he has total control over all things football, and then some.
It's going to be an interesting dynamic though. I see a lot of similarities between Mourinho and SAF, but there's the obvious differences as well. But for the (major) lack of a better option and LvG's struggles, I think we need to approach Mourinho. Even if it's just to get the club back on track, especially considering the quality of managers coming in over the summer.