Interesting point. Trademark registrations have to be renewed every 10 years and part of the renewal is alleging and proving that the Trademark is still in use. Use in the Trademark sense means, for goods (if goods are what is recited in the registration) selling product bearing the mark in interstate commerce. For services, it means advertising the services in interstate commerce while being ready willing and able to deliver the services.
The basic registration for the Oilers is this one. https://tsdr.uspto.gov/#caseNumber=73104154&caseSearchType=US_APPLICATION&caseType=DEFAULT&searchType=statusSearch
The mark is "Houston Oilers," words only, no logos, for the following services:
EDUCATIONAL AND ENTERTAINMENT SERVICES IN THE FORM OF PROFESSIONAL FOOTBALL GAMES AND EXHIBITIONS
That's pretty standard for a football team registration. Or any sports teams, sub out "football."
So, the last time the registration was renewed, this was submitted as a specimen, that is proof that "Houston Oilers" is in use. https://tsdr.uspto.gov/documentviewer?caseId=sn73104154&docId=SPE20180105155702&linkId=2#docIndex=1&page=1
It's a page from the 2017 Tennessee Titans Media Guide showing the logo history of the Oilers. That ain't advertising football games and no one is ready willing and able to provide an Oilers football game.
That's pretty much not trademark use, even for the loosey-goosey standard for service marks.
So, if someone were so inclined, I think they could cancel this base registration pretty easily because it's not used on the services and therefore abandoned.
What you also notice, though, is that the attorney is not for the Titans, it's for "NFL Properties." That tells you that the league really controls the trademarks and team names and they're not about to let the Texans or anyone else revive the Oilers name, whether the registration could be cancelled or not.
Note also that there are registrations for "collateral goods," like team apparel. The Titans/NFL still sell Oilers gear, so the mark is actually in use there and not abandoned.