Q:
Do we have to start over again?
A:
All guild benefits are server tied. If he moved but you are on the original server you still have access to all the benefits such as a guild stash if you had one.
If you all moved then yes, you will have to start again. All guild related stuff are server tied.
If you are still on the original server I am stumped as our Operation: Union has multiple guild stashes all over different servers and they are tied to that particular server.
https://forum-en.gw2archive.eu/forum/game/players/OPERATION-UNION-Bringing-Players-Together
Glitch is correct. You should still have your guild upgrades on the original server. If your guild bank is now empty, that means your leader took everything with him when he transferred. If you transfer to a new server, you’ll need to earn influence and unlock your upgrades again on that server (but you’ll never loose the upgrades and influence from your original server).
P.S. I believe mail is cross-server. So while you can’t access the guild bank on a different server from your own, someone on that server could pull an item out and mail it to you.
Thank you guys for this information, your answer help me a lot.