First off, if you're not flat-out telling someone to kill themselves or goading them to do so, then it's not a crime, because suicide is not a crime, hence you're not abetting one. I'm aware you already said it's not a crime and that you're not concerned, but it leads into the next point.
Second, since it's not a crime and you haven't committed one by goading, then I think the police would have sufficient evidence for their investigation of suicide based on the member's SS activity, as well as other activity that would indicate you weren't communicating with them off the site. So there's no reason to contact you personally unless they want to intimidate you for a pro-life agenda, and that's some Big Brother shit I haven't yet heard of.
If you're not using something like a TOR browser to hide your IP address, then, in theory, if the police wanted to investigate the death and come question or harass you, they could (edit: after getting the IP address from the site owners, no word from them as to whether they give the police information without warrants). So far, no member has ever reported the police showing up and questioning them like this. That doesn't mean it hasn't happened nor that it won't, but I think of all the ballsy members we have who would be affronted by this and want to make the forum aware, just like some have posted when their N was confiscated.
I think it's good that you asked in order to address your anxiety and alleviate it should it not be something to worry about. Lots of folks here have the same fears, and I've noticed similar questions and concerns are occasionally posted.