1) Is blade chassis connected to the same 3750 switch or to the other (RSPAN destination) switch?
2) If blade chassis is connected to the other (RSPAN destination) switch is RSPAN vlan permitted on link between the 3750 switch and the other switch?
3...
From my experience you'll not loose any data. But you will need resize LVM group in order to make available new disk space to underlying Linux OS. You need to open case in TAC to do it.