Every minion made by the Gridanian goldsmith (you know the one)

[Cleretic]

I don't think he actually disappeared into the rift, but pulled an Estinien. Do we have a timeline of his makings?

Here's the very rough timeline of what we know about the Gridanian goldsmith.

1. Lived in Lapis Manalis, made and maintained the Galatea, in particular the Galatea Magna.
2. Leaves Lapis Manalis to pursue 'beauty'.
3. Meets and becomes infatuated with Lady Amandine, the Haukke Manor boss.
4. Performs a voidsent summoning that gets pretty awkward for everyone involved, in part because he summoned a mindlfayer we met in Zero's Domain.
5. Creates at least some amount of the known mammets. (This may have started before 4.) Thanks to 3, it's a reasonable assumption that the Wind-up Succubus was an early one.
6. Gets arrested, tried and eventually hanged for occult rituals; plausibly the one mentioned at 4. This is when most of the mammets are discovered.
7. The Puff of Darkness is discovered at some later point and other location, leading to exhuming the coffin and finding it empty.

So, he was killed and buried. Or at least, managed a pretty good show of looking like he was killed and buried. So either he faked his death, or overcame it; for most of the game's life the former was the far more likely of these, but with the advent of Lapis Manalis suddenly the latter isn't off the table either. Certainly, Galatea Magna shows he's capable of making something convincing enough for the job.

[Iscah]

Certainly, Galatea Magna shows he's capable of making something convincing enough for the job.

He couldn't have faked his death (or at least his burial) with an automaton copy though, or it would still be in the coffin when they exhumed it.

A bit of a missed opportunity, maybe - it would certainly be a neat twist for that to happen. Though it does give a different vibe of "exceedingly clever" rather than "must have invoked dark arts".

For the empty coffin, if he didn't really get buried and then escape it somehow, it would probably require something like an aetherial illusion-clone that will dissipate into nothing later.