A lot of their military has basically defected though
Bigger problem than that is they are broke.
The Russians can afford a small war, the Ukrainians can’t.
Pravda Russia Today says Crimean units have. But non-Russian outlets report that there's a standoff, with Ukrainians not shooting at the Russians (presumably under orders), but not letting themselves be disarmed by the Russians. The Ukrainian government is apparently trying to avoid war, while mobilizing reserves. Russia has been mobilized for a while, presumably for something like this.
Ukraine won't kick anything off for a while. It took almost 6 months for us to get ready for Desert Storm. I expect it will take a few weeks, minimum, for a shoestring budget peacetime army like Ukraine's to get ready. It took Afghans almost a decade to turf the Soviets. This isn't going to be a lightning war, any more than our campaigns in Iraq or Afghanistan have been lightning wars. If Ukrainians want their territory back, however, they will need to fight for it.