There are basically two options of what you can do when you time runs out and can't pay for it straight away.
Here they are :
1. Just wait until you can pay again (probably getting really anoyed because all your mates are raiding without you)
2.Join a Private Server temporarily play there?
Personally I play on a private server (the normal ones that don't get you to 70 straight away as I love a challenge) but I would love to know what you do as I havn't seen any posts like this here and it would be quite interesting to find out