If Putin does that, he has to distance himself from the legitimacy of a separatist Eastern Ukraine, which would be counter to everything he has said previously.
It could potentially be seen as a sign of weakness to do this.
Its also not inline with his ambitions regarding a Russian sphere of influence.
It could be a potential face saving option, but I think it unlikely that he will go that far.
There was talk that Russia could veto the UN security council meeting that the UK has called, but I think that unlikely as that would be seen as obstructive. The mentality being they have "done nothing wrong and have nothing to hide". However I think they could be more obstructive on the ground instead and pay lip service to calls to do X, Y or Z.
I think if its a cock up (which is the most likely option) there will be traceable evidence which will be difficult to cover up. But not necessarily enough evidence to get an admission of guilt or prove who is responsible beyond doubt.
If Russia are responsible, their best option would be to be seen to cooperate to a point, but generally be difficult and obstructive at the same time.