Honestly it would be so funny that Little Mac is forced to essentially continue the war because the South simply does not accept any of his generous peace offers and he can't chicken out of the war either, although it makes me wonder what sort of possible reconstruction could happen under him.
McClellan would really be helped if he were a politician rather than a manager. His own party has a view that peace is good, but what
sort of peace is a very different matter indeed. Meanwhile, the split Republicans could live with peace, but not one that protects slavery as McClellan intends to do. If McClellan could weld the War Democrats and the moderate Republicans into a temporary coalition to force through this effective white peace - or even to back his continuing of the war - then he could actually sit on solid ground for 1865 until the House elections of 1866 to set policy.
However for Reconstruction, it's basically what he proposes there. A white peace and effectively a status quo antebellum politically, but with new state representatives from the governor on down, and only brief interruption to the process of running the states.
Certainly he's open to punishing people who rebelled (and that blanket amnesty definitely won't apply if war resumes) but he has no interest in wholesale punishment of the Confederacy. He'd be more lenient than Andrew Johnson that's for certain. Above all, he and many other Democrats, were trying to avoid a social revolution that the Emancipation Proclamation represented, it was why they used extremely racist propaganda in much of their electoral language OTL (and to be fair, TTL, I simply don't wish to use it here).
Either way, he's slowly backing himself into a corner to do things he didn't want to do in the first place, despite thinking he's coming out ahead.