There will not be any issues and programming can be attempted again once power is restored as long as the feature row has not been reprogrammed. If the feature row is not altered, then there will not be any problem in making another attempt at programming the XO2 using I2C. If the power loss occurred while the feature row was being accessed, then there could be a potential issue if the feature row reprogramming disables I2C and you only have access to this port on the board.
Lattice recommends that field reprogramming be done in a manner to avoid alerations to the feature row. If it is required to change the feature row, it is recommended to perform this last in the reprogramming sequence.
Please note that if the feature row becomes erased, all configuration ports are active upon power up. Therefore there will not be any consequences from the power loss.
Please see "MachXO2 Programming and Configuration Usage Guide" for more details pertaining to I2C default conditions on page 14-23.