Hello Samir
Yes you are correct that using a rib-scale of 128 may still not be enough to scale down the metric so that it fits into the 32-bit value of the routing table. Whenever the value exceeds what can be accommodated, the metric installed is a metric of infinity.
The rib-scale value is 128 by default, and works for most EIGRP networks. For some extensively large networks, you may find that metrics of infinity will be seen more often. If this happens, you are able to modify the rib scale value. This can be done using the metric rib-scale command. For more info on this command take a look at this Cisco command reference.
I hope this has been helpful!
Laz