I think it would be a healing ritual
for the MO community for someone of appropriate stature (which excludes me)
posting an inviting *cwiki* question that elicits responses from the users
to this significant passing,
the equivalent to mathematics of Bill Thurston's untimely death.
The (useful) notice,
[Grothendieck -sad news](https://mathoverflow.net/q/187106/6094),
doesn't quite achieve it.
Perhaps something along the lines of Dave Roberts' query in the comments...?