I'd say it totally depends on whatever you were on probation for. Formal or informal? Felony or misdemeanor? Federal or State? If State, which state? Basically it boils down to how bad "they" will want you back. More than likely, if it's a absconding warrant with a $20k bail, it is not "end of the world" serious or there would be no bail or a much higher bail attached to the warrant. So "they" will be content to let you be for now and pop you first time you ever show up at US immigration.

In any case, unless you intend to outright forget about your US citizenship and never return to the the USA ever ever again, for the rest of your life.... you need to deal with it. I imagine the best course of action would be to hire a lawyer in whatever jurisdiction issued the warrant, have him appear for you and try to get the warrant recalled and a new court date set where you can return and deal with it without being popped at the border by US Immigration.

Life as a fugitive sucks. I image if you stay away from the US you would be fine up until whenever your US Passport expires. Then unless you are a duel citizen and can get another passport that will let you travel as freely as a US passport, you're kind of stuck in a REALLY messy situation.