Brewed a nice RyePA last weekend and I just opened the fermentation chamber to find the airlock not bubbling. A quick peek at the wort confirmed a nice krausen in place. I pulled the airlock and noticed the grommet wasn't seated completely and in my effort to fix it, it fell in the beer. So what to do now? It feels as though I should leave the grommet and take my chances given it was sanitized a few days ago. Second question - I don't have another grommet on hand so at the moment the airlock is seated tight against the lid. Thoughts on how to handle that?
The only issue with the grommet falling in is possible contamination depending on if there were any organisms on it (probably) and how strong your ferment is - sounds like you're at low or high krausen so you should be ok. The larger your yeast population and stronger it is, the greater chance they'll outcompete anything that gets in there at this stage. You won't pick up any off flavors from the rubber.
The airlock is just a convenience to give you a visual indication about the rate of the ferment. I.e. it's not necessary. You can just sanitize some foil and cover the hole or use a bit of paper towel. The important thing is to keep the hole covered so nothing floats/crawls/flies in but not sealed so that CO2 can still escape.
The grommet is already in the fermenter now so I wouldn't worry about trying to get it out. That will increase the risk of infection.
If you cleaned and sterilized it only a few days ago it should be fine unless you were touching it with dirty hands or a bug landed on the grommet or something like that.
The airlock is meant to be a one way valve that lets the co2 escape so if you have managed to get the airlock tight against the lid the seal should be fine. You can try to use some vasoline to make sure it is really airtight if you want but probably not necessary.
A grommet doesn't cost much so you could probably pick up a spare one and put that on if you really want to.