Fatty those bases don't usually stay closed for very long (somewhere 5-8 minutes).
If you close the last two bases of a country's, they couldn't launch until a base would open.
But then again most likely a capture would occur shortly, and the map reset. So it would actually be beneficial to the team down to two bases.
Plus there is no incentive to keep an enemies last two bases closed, other than for capture, because its boring for the side thats winning. Pilots are much more likely to keep the ack down and vulch the last two bases.
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Vermillion
**MOL**, Men of Leisure
"Desperately trying to figure out why Kamikaze Pilots wore helmets"