In the original plans of a couple of years ago relegated WT teams would get 1 year of auto invitation as well. Not sure if that still applies.
now that you say it, I remember reading sth like that back then as well, but it's not in the rules. In contrary, for the "best UCI ProTeams" wildcard ranking "teams registered as UCI ProTeam or UCI WorldTeam during the previous season are taken into consideration", so relegated teams need to earn their spot as well
just read an interview with Guercilena from Trek, and he also said "the first to be relegated remains in the WorldTour circuit as a wildcard for one season" - but as mentioned above, I really see no indication for that at all in the rules.