The other answer is good for cutting the baseboard in place.
However, in most cases this should never be done. Unless you simply don't care about how your baseboards look this is a bad decision.
An oscillating tool cuts using vibration and pressure. It is not going to cut a thin straight line even if you are very very skilled at using it and have a new blade and so forth.
If you are doing this on both sides of the wardrobe I cannot fathom that this would be quicker than pulling baseboard out and making two cuts with a table/circular saw and reinstalling. In a lot of cases baseboards will have a few finishing nails and if you carefully pull it out you can realign the baseboard with the same nails/holes. If it is just glued then reglue.
What I am saying is the oscillating tool is your option but no one who wants to do quality work would choose that nor would they believe it saves them time. When taking out baseboard you can basically pull them while only damaging the area that they cover. Get a joint compound knife - 6-10" - and slide it behind baseboard until you get a gap good enough to put a decent lever (bar, big screwdriver, whatever), push baseboard a little further from wall, and once it can be wiggled a little use your hands to pull it out starting from the gap and working your way out with small tugs.
I would also recommend putting your wardrobe in place before doing your reinstall so that you can be sure your baseboard cuts are correct.