Oxidization ruins wine. Does refrigeration stop oxidization? No – it only slows it down, and that only because cooler molecules move more slowly. Does prolonged storage of wine at temperatures found in most refrigerators permanently degrade the quality of most wine. Yes – I firmly believe that it does.
Use some wine-preservative gas to better preserve your fortified wines and aromatized wines (vermouth or quina). It is heavier than oxygen. It has virtually the same make-up as the gas that was in the head-space of the bottle of vermouth wine and kept it fresh until you opened it.
Get some wine-preservative gas from a wine shop or online. Use it to reseal the bottle free of oxygen. Store the bottle protected from sunlight and removed from any source of heat.
Stop being a barbarian and get your vermouth wine out of the refrigerator!