I sent an unsolicited email to the person above, and was polite about asking, but no reply yet :)
The comment I linked incidentally happened to be (understandably) stuck in my head, but some bumbling around and experimentation with Algolia for a few minutes (trying keywords like "works at", "engineer" and "dev") also found https://news.ycombinator.com/item?id=29700627, https://news.ycombinator.com/item?id=12924580, https://news.ycombinator.com/item?id=12928349, https://news.ycombinator.com/item?id=20701499, https://news.ycombinator.com/item?id=19815847, https://news.ycombinator.com/item?id=16971725, https://news.ycombinator.com/item?id=3587191, and https://news.ycombinator.com/item?id=4728531. It's quite possible none of these are relevant or useful; I also just thought of https://github.com/search?q=tumblr&type=users, which surfaces an interesting level of signal right on page 1, and this is not even mentioning LinkedIn, notwithstanding that site's caveat of "oh no" vs "likely most direct solution to problem" :)
(Now to work through this small pile of unrelated interesting things that also mysteriously opened themselves over the past few minutes. Welp. All good :D)
That comment was from a few years ago so the poster may be relatively distant to Tumblr nowadays and it might take a few additional people-hops (if it doesn't fall through) to get anywhere. I also wonder if old/deactivated non-public account data is held indefinitely (eg, private messages)... it probably is...
Regarding Stripe, wow, I admittedly didn't quite read the name the first time through the paragraph, and was very surprised when I actually noticed ("...that Stripe?"). I guess it makes sense; they're similar in scale and incumbance to the big-N stuffy local banks now. A good reminder that class-leading web design isn't necessarily a function of broad-spectrum competence across the board, just a very well-paid design team lol
I take it you can't reopen an account? :/
(Uh, if you'd even want to...)