I took 15 years off. I left right before my 2nd dan test (went away to grad school), and just started again about 15 months ago.
Had I went back to my original school (or another in the same organization), I'd have kept my rank and not tested until I was ready to promote. My former Sensei moved the dojo I used to study at about an hour away, so that wasn't an option. Another school in the organization offered to let me keep my old rank, but I told them I didn't want to. I didn't end up going there for other reasons unrelated to rank.
My current school has very close ties with my old school. My old organization's founders came from my current organization. They kept 90% of the curriculum.
My current teacher told me I couldn't wear my old belt in his dojo. My response was "I don't want to; all it'll be is a Halloween costume at this point."
I started over as a white belt, and I'm currently a 4th kyu. I know all the material up to 1st dan, but I don't care about being a black belt. I can "beat" several black belts I train with, but I don't care. I've helped several students who outrank me with material for their rank, but again, I don't care.
I genuinely feel I'm better now than I was 15 years ago. I left at 24, and will be 40 next month. I'm smarter, stronger and faster now. The only thing I'm not better at is flexibility.
How do I feel about being a 1st dan? Been there, done that. I chased rank when I was young. I'm currently chasing improvement. Would it be fun to work on the material I did when I left? Sure. But it's not going anywhere. I'll be better at it when the time comes.
There's nothing wrong with wanting to keep your old rank. But remember what you're really after. Is it a belt, or is it ability?