To be fair Shane Richie wasn't too bad at all on the EastEnders bits over the last couple of years - and he'd be a much better option than Grimshaw and already part of the night.
The team is already quite young already so I think it's a more senior presenter they need. Huw Edwards wouldn't be a bad shout, though whether the BBC would permit their senior news anchor to host their charity telethon I don't know. Chris Evans another possibility - there is no TFI Friday tomorrow.
It does highlight though how they've completely failed to line up a successor, something other BBC shows have been quite good at doing in recent years. Fearne Cotton has now been involved for longer than Gaby Roslin was but isn't anywhere near as associated with is as she was. At least with Terry and Gaby it was Terry and Gaby but in recent years it's been Terry and any number of female co-hosts, making replacing Terry even more difficult.