Most of their servers are encrypted I imagine, so a seizure just means a TLA gets a bunch of encrypted disks to have fun with. My only worry is that a TLA can just ask for the keys to these disks and get Riseup rubberhosed¹.

¹ — https://en.wikipedia.org/wiki/Rubber-hose_cryptanalysis

Worth reading up about Key Disclosure Law too: https://en.wikipedia.org/wiki/Key_disclosure_law