title_body: What if beer (opened) was left in fridge for like... months
upvoted_answer: Your question says they were opened?  I'm going to venture probably not.  You tagged this 3.2-beer, does that mean these are low alcohol session beers somewhere around 3.2% ABV?
  
  If the beers aren't moldy, best case scenario is you now have two bottles of home made malt vinegar.  Make a balsamic, have some steaks with side salads.
  
  If they were closed or sealed in any way, they're probably fine, though depending on the style they probably won't taste great.  Low alcohol and hoppy beers don't age gracefully.  Higher alcohol or darker beers often do better with some time on them.  But either way you have to keep them away from air, namely other microbes and oxygen or else things go downhill real fast.