It's hit or miss and very much depends on the condition of towers in your area, whether they have battery backup, how many people are connecting to the towers during loadshedding etc..
The only people who can tell you, are those in your nearby vicinity who already have fixed LTE..
Simply doing some speed tests from your phone during loadshedding would also give you some indication of what to expect, but take the results with a grain of salt, since there may very well be different QoS for fixed LTE..
In my area, I go from full bars on 4g to maybe one or two on HSDPA+..