Right, the Republicans will be blamed whatever happens. But if the Republicans just vote "present", rather than endorsing the President's "plan" and make it clear they oppose it, they can not be blamed for the consequences re the "fiscal cliff".
They need to start setting themselves up for the 2014 elections, to try to regain the Senate. Most important is to regain control of the debt limit. We can not force the Senate or President to agree to a specific budget. We can tell them, "OK, you can borrow $750 billion this year (not $1.3 trillion). Spend it as you will, but when it's gone, it's gone." Come November, when the cupboard is bare, the President may be a bit more pliable.