Precarias have to be renewed prior to the expiry date. This requires the applicant to request the renewal no earlier than 10 days prior to the expiry date. It is quite normal for a precaria to expire without Migraciones having completed its processing of the application. (In some cases the precaria needs to be renewed several times while Migraciones drags its feet.) You don't have to go to Colonia, but you can't just do nothing either. I think you need to formally request renewal of the precaria: go into your case on the system and press the button at the foot of the screen ("Solicite renocacion de su precaria") that requests renewal of the precaria. Then check each day to see that they have issued you a new precaria in the system (it will be downloadable and printable) with a new expiry date. If you don't see this after a few days, you should probably go and talk to them in person. I believe there is a short grace period after the expiry date to still renew it. If you don't do this, I think your process will lapse and you may have to start all over again.
(The above applies for non-Mercosur. If you are Mercosur, perhaps things work differently.)