It might be better to focus on Syria for now.

Removing Assad from power especially in advance of any negotiations (and in fact it's a regime, not just one man) just isn't an option, without the overthrow of the government by the opposition - in which the only really effective bunch are really Isis and al Qaeda, or by outsiders. (Apart from the Kurds) Which really isn't on. (Even if it was the precidents of Iraq and Libya aren't exactly promising.)

It's not going to happen, and insisting on it merely guarantees the war cobtinues, or that Assad, with Russian support, defeats the whole bunch of opposition, including Isis.

It would be possible to negotiate round aims such as supervised elections, including the exiles- who of course the regime is not in a position to control. In fact that's been offered and rejected so far. The thing is, the Russians exert a lot of influence, and peace is very much in their interests, and Assad is probably dispensible to them. There are people in the opposition who likely would come on board for a settlement.

An outright victory for the opposition, even if possible, would be likely to end in something akin to Libya, with sectarian extremists running the show in so far as anyone ran it.