Correct, in case blockstream stops giving service you would only have to restore the seed in another wallet or operate in the other mode that Jade has which is air-gapped (like seedsigner).
There is no risk of loss of funds.
On the other hand you can set up your own server:
https://help.blockstream.com/hc/en-us/articles/12800132096793-Set-up-a-personal-blind-oracle
You also have it on Umbrel: