The eng 1 N2 tachometer indicator may be inoperative but the N2 tachometer generator for eng1 must be operational for dispatch.
The fact that the N2 tachometer generator is operational can be verified by checking the AVM analyzer for coresponding fault code (not a pilot job) or by checking at start that engine start switch automatically move to off.
After that it's no way to check if it fails.
If the tachometer generator works it will send the signal that the engine failed,and the gear will be raised by the LGTU at a NORMAL rate. The hydraulic liquid used to raise the gear (from sys B ) will be lost.