Most likely because the duration they're bound is constitutionally based. If not that, once it's severed, the Lib Dems disappear without trace if Clegg doesn't go, which he must. They've been well and truly shafted, but so has Cameron not done his party, or this country, any favours either. Maybe the prospect of another hung-parliament plays a part too. There has to be some pretence to a functioning democracy, with active, cohesive parties contributing, which the Lib Dems won't be if they withdraw.
Most likely because the duration they're bound is constitutionally based. If not that, once it's severed, the Lib Dems disappear without trace if Clegg doesn't go, which he must. They've been well and truly shafted, but so has Cameron not done his party, or this country, any favours either. Maybe the prospect of another hung-parliament plays a part too. There has to be some pretence to a functioning democracy, with active, cohesive parties contributing, which the Lib Dems won't be if they withdraw.