Russia steps up its aid to Transnistria. They may have intervened, but given the state of the Russian Army during this period, I wouldn't bet on it. Back then, the Russians had a decaying military in horrible shape. Even now, with their increasing military power, they still hadn't fully recovered from the degradation of the '90s. Remember Georgia 2008? You don't hear much about it, but their military performance was actually very sloppy.
If the Russians did intervene, they would send in overwhelming numbers of troops. Due to their military incompetence, they will suffer many casualties and battlefield humiliations. Russia will, of course, be universally condemned. After all, they're illegall invading an internationally-recognized part of Moldova to support secessionists, but they'll of course veto any proposed sanctions at the UN, so no one will even bother trying to table such a resolution.
If they don't, the Moldovans and Romanians crush the Transnistrians in a matter of weeks. It doesn't matter how much military aid and volunteers they get, they cannot stand up to two armies. And I would suspect that the Romanians would drive up Transnistria's borders and close them off to cut off Russian aid.
Russia would probably bring horror stories of what is happening to civilians in Transnistria to the UN (even with the Moldovan defeat, they still claim that the Moldovans committed atrocities in Transnistria), and they will claim that a people's right to self-determination is being violated. They will propose a referendum for Transnistria depending on what they think the vote will be, and attempt to get sanctions imposed on Moldova and Romania. The US, seeing this as a Russian attempt to "divide and conquer" the former Soviet Union in order to weaken a former Soviet republic and get a new client state smack dab in the middle of the FSU, will veto these sanctions.
Overall result; Transnistria is today a part of Moldova.