what is the impact on Active and standby node if logs of Quorum Journal node gets full?
One or all of them?
One shouldn't be too much of a deal. It should be like a failed node and as long as a majority of QJMs still are able to write there should not be a huge issue.
If a majority of the QJMs run full the namenodes would not be able to make any write transactions anymore. Read-only access should still work. Now I am a bit concerned if edit logs could be corrupted. I had a zookeeper node run full once which resulted in corrupted edit files and the inability to startup again till I deleted the file.