I am a finishing graduate student after, what I personally would say, a rather mediocre PhD (mathematics).
There has been some personal issues (mental health issues) and so I could not perform to the utmost of my abilities. The PhD will, however, still very likely be finished. The mental health issues have improved.
Regarding the question of continuing with research my supervisor has claimed that there is an agreement with another university to trade finishing PhD-students for post-docs and my impression was that a post-doc was essentially a guarantee. (However other faculty members do not seem to believe that I am cut out for this and the argument would be that my supervisor, having had no prior graduate students before me, is not experienced enough to accurately decide this).
So I ask:
When is it not a good idea to continue with research after the PhD? Are there any traditional red-flags?