I think you say No and No for the moment.
Eli is currently surrounded with no run game, a porous Oline and a Dline pass rush that is no longer dominant at the moment. The same Dline that helped him get those rings. What is behind Eli at the QB position on the bench is no better. I think you have to let him keep playing with the understanding that he is surrounded with nothing other than some good WR's.
Coughlin only goes if Mara thinks that Cowher wants the job, which he does or at least says he's always dreamed of. The question for Mara is, how rusty would Cowher be? It's been some time. Do I trade that for Coughlin? If I'm Mara I let Coughlin finish the year, see how it goes and if needed you move on from both Coughlin and Cowher. Giants aren't going to tie themselves to media pressure in regard to filling the position.