Assuming these are M3s, yes, you can enable centralized licensing in 6.3.x. IF that master controller goes down, the aggregate license pool is available for 30 days post failure. This is assuming your 1st scenario with 2 controllers (Master/local).
Once you break out to dedicated masters, then they will be in charge of the management of these license pools. The same failure scenario applies however. IF BOTH masters die (extremely unlikely), then the 2 locals will have 30 days of ability to use the centralized licenses.
IF it takes you longer than 30 days to restore your mobility network, we have other issues to talk about :-)