When the enemy gets early mothership, and uses vortex to suck in half of your army, what do you do? I usually stuff all my units into the vortex to prevent them from getting seperated so that I can deal maximum damage.... But then they'll destroy your base. If you try to attack, you'll get easily overpowered because half of your army is inactive while the enemy has full force... What do you do in this case?
If you scout it then having some VRs will help kill it fast before it casts vortex, OR waste it on the VRs to save itself so you don't get that vortex back in base... If the mothership is early then chances are you'll have better army so if part of your army is sucked you can still fight with the rest... Or back off for a while till the vortex ends... Or if you have some sentries you can delay him with sentries FF... I don't think that there's a clear answer to that, since it's dependant on how fast the mothership is, what tech you're going, on which map you're playing etc... If you had any recent match where this was used against you you can always post it here and get some tips on what you could have done better in regards to the mothership if you're not 100% sure of your own judgement...
If the Protoss has no archons or colossi, you should throw the rest of your army into the vortex. It really doesn't give the opponent very much time to destroy your base, the best they can do is retreat. However, if he has lots of archons and colossi, DO NOT run the rest of your army into the vortex! Your units will be so clumped together when exiting the vortex, that enough archons and colossi will instantly kill your entire army.