I would say that it is never wrong to check any viable scenario, but in terms of sizing the only accumulations into the suction drum would be the fresh feed and the power input from the compressor. The amount of fresh feed coming into the system during a relief case should be known to you. Since the recycle flow to the drum ultimately comes from the drum, there is no additional material accumulation due to the recycle, however, the power input of the compressor could be significant- i.e. in the extreme case of total spillback without an aftercooler, the entire power input will be manifested as a temperature and pressure rise. Even if there were no fresh material entering, the energy input would have to leave the system through the PSV.
These are just my thoughts. Best wishes, sshep