Hello dear community,
I spend nearly three years within my current guild. During this time I’ve collected a lot of guild seals. Now it’s interesting for me to know if these seals are bound to my account or to the guild. I want to avoid losing them in case that I decide to leave the guild some day…
with regards Garland
You keep all your collected seals, I believe, same as you would keep any keys from guild tasks.
Once they’re yours, they’re yours.
I can test this for you with an alt, if you like, and if you remember to remind me tomorrow 
Nothing gets lost - I’ve switched guilds and still have all my seals.
Keep in mind whatever you earned in one guild will be deducted from what you can earn when you switch (for that week.)
If you earn 500, then switch. You can only earn 1500. 500+1500. Will reset when the week is over.
I mention this because pf guild reqs. Inform your new gm that you had earned then prior to joining.
As the others said you don’t lose any from your total collected.