Oh that's an easy question to answer (from a Texans fan's perspective of course).
Pay him and keep paying him. I say they continue to give him top-dollar money for as long as he wants to play the game. I mean, think about what's he's done for that organization for just a moment. He's meant everything to them over the years and they all love him so much. I'd personally like to see them give him the highest paying contract a running back has ever seen and then honor that contract to the very last year of the deal (preferably something in the 7 year range just to make sure he goes out a flaming meatball of course).
Just to show him how much he means to them I'd also like to see them use their franchise tag on him every season for as long as he continues to play there whether it's needed or not. It would give him a warm feeling to know the team needs him that much.
They should hold on to him (and pass on any other great backs available in the draft) until he becomes the all time rushing leader even if it means slogging through some seasons of 1.2 yards per carry to get there and being forced to let other players at other positions go due to cap constraints. It's for Eddie after all so it's worth it.
That's what I'd like to see. If they could hang on to Steve McNair another ten or so years at top-dollar numbers to show their gratitude to him as well that would also be nice.
Fitz makes bad decisions. That's not going to change.