I am sorry to hear about Ron Graham. Best wishes to his friends and family.

The bulk of this answer will address the general question about if or how MO should memorialize mathematicians when they pass away. I believe that a community wiki question on MO about a person's mathematical achievements and/or legacy is, generally speaking, an appropriate and and actively positive use of the forum. My arguments, in no particular order:

**Consistent with MO mission**

Reviewing a successful mathematician's contributions is by definition research-focused, and it often gives an interesting glimpse into connections between the different ideas that the person worked on. The questions and answers should stay focused on mathematics as much as possible, but this hasn't been much of a problem in past examples.

**MO is the best forum for this**

It is normal for articles or blog posts to be published when a prominent mathematician passes away, and these are certainly valuable, but MO posts often attract a good diversity of perspectives on a body of work that is often not well replicated elsewhere. And MO answers are more likely than some other sources to get the mathematics right since there is no pressure to translate technical ideas into language suitable for a general audience.
Sometimes mainstream press even links to these MO questions for this reason.

**MO tributes stand a reasonable good of being tasteful**

MO has policies against gossip, innuendo, rumors, and personal remarks, and these policies provide some assurance that memorial posts will not go astray. MO should of course heed the wishes of surviving friends and family one way or the other, but a priori I don't think that it is disrespectful or exploitative to acknowledge and celebrate someone's contributions on the internet. Caution should be exercised in cases where the mathematician had a rocky or controversial relationship with the mathematical community, but I think the risk is low in most cases.

**The risks are low**

So far as I am aware there is no explicit rule against these sorts of questions currently, so if there were a high risk that they would be abusive or disrespectful (or perceived as such) then we would probably know about it by now.

In memoriam. I am not a professional mathematician, and I assume that my views/ideas maybe aren't acceptable for the community. This thread while it is legitimated by the copyright could include the material/sources in discussion about, mainly, the more important work of a mathematician in a concise and inspiring way (to young PhD students and other). Then the best/recent answers are added to the Newsletter of MathOverflow if it is possible (is a periodic publication). $\endgroup$ – user142929 Jul 8 at 11:50In memoriamof the chat (if it is legitimate in this MathOverflow) $\endgroup$ – user142929 Jul 8 at 11:50In memoriamwhere the comments can be moderated. Of course, feel free to remove my comments if aren't suitable in this thread of Meta MathOverflow. These and previous are just my ideas that I evoke, I add this last phrase as disclaimer since I don't know what can be a legitimate activity about this concern $\endgroup$ – user142929 Jul 8 at 12:20Ron Graham passed away on July 6, 2020. (...) What the community could do right now to remember Ron Graham and to commemorate his outstanding contributions to mathematics". Now there is a MO post about this mathoverflow.net/questions/365170/…. In case there is still a need to address this question in Meta I'd suggest to repost it separately. $\endgroup$ – YCor Sep 12 at 11:02