I think you bring him back. Relievers are (variable, fungible, a crapshoot, pick your favorite word). That fact that he's bad this year might be the best reason of all to bring him back, unless you are certain (given his age) that he's in full decline or injured. He pitched almost 80 innings in 2018 so maybe the best thing they could do with him for next year now is use him less.
And if he doesn't return to form he's still cheap enough to release mid-season (unlike all the guys we had this year).