In this case, it's wrong to omit "rather" because it won't sound right. (It doesn't sound right to me as a native speaker.) This is because "than" is not preceded by a comparative (or followed by one, if the order is inverted). There needs to be a comparative, such as:
Getting up early is better than rushing at the last minute.
Compare these definitions for than and rather than, for example.
Here's a little history, as a bonus:
A very long time ago, it would have been OK to omit "rather", such as in:
The Apprentices being encouraged herewith [...], than to do nothing, brake open some Prisons.
The life and raigne of King Henry VIII, 1649
It looks like this construct was last used sometime in the 1600s (and at that point, as you can see, spelling and capitalization were a little different than they are now). The passage itself does sound very weird to me.