The only worry with an IPA is that the hop flavor and aroma will break down, +1 to the dry hop again. For almost every other beer you can just leave it for a very long time. Someone in my brew club left his beer on yeast for 1 year, came back and said it was wonderful.
Actually a question about this. I asked this a while back and never got a response. For an Imperial style beer, it takes quite a long time to mellow generally. Does this mean that when doing a beer that you want serious hop aroma you dry hop a week before bottling? Also what happens with the flavor and bitter compounds over significant time, like 6 months? Will the hops still impart the same bitterness AND flavor? I would expect bitterness to be about the same since iso-alpha acids are very stable, but what about all of the wonderful flavor compounds?