this article could use more info by alien-experts
“Sudden death” is a special mode that starts when a match has already taken a long time. How long this time is depends on the server – on most servers it's somewhere between 30 and 50 minutes. Sudden death is intended to make a match finish quickly, by adding some restrictions to game play. On many servers, few minutes after sudden death kicks in the match is stopped anyway by reaching the time limit.
The effects of sudden death are:
When sudden death starts, all players get a warning message on their screen, and on many servers there are also prior warnings.
First of all: DON'T PANIC! – except when you are a human with a bad team, which is the common situation for human players
If you get the first SD warning, quickly make sure that:
During sudden death, you have to be extra careful for your buildings. It is useful to have at least one builder hanging around and repairing damaged buildings. If you're on human team, especially take care of armory, and also of defense computer, medistation and telenodes. If you're on alien team, especially take care of your eggs.
On the other hand, SD is indeed a good chance to finally get your victory! If you are well prepared and time it well, you can rush the enemy base just in time to destroy some crucial structures. Also remember that every destroyed structure is a win – so if you can spare the credits it might make sense to do some “kamikaze” attacks to take down some enemy defense structures.
Actually, there are some structures that can be built during SD:
On some servers there are variations of the SD rules. For example, there's a variation where humans get the build points for a destroyed armory/medistation/defense computer back and can rebuild these. This is meant to make up for the fact that humans heavily rely on these buildings while there are no similarly important structures for aliens.