I know it appears now like a bad move, and I do think Chelsea should offer him a new, much revised contract, but if you sign the likes of Isco, or hell, a cut price Modric to replace him then I don't think the disappointment will rear its head next season.
It's romantic to want your most loyal servants to stay on, but there comes a point when clubs and players have to move on. Lampard definitely still offers something to the team, but we don't know if he wants to play more than he does now, and if the management team want him to play less.
Like I say, I think as it stands it looks like a bad move because of your clear lack of creativity in the centre. Bring in a top talent in that department, and the allure of Frank Lampard as a playing figure might recede.
It's nice to want him around as an experienced head, but perhaps he wants to be seen as more than that. We saw his frustration during AVB's tenure, perhaps he wants to still play every game.