NO NO NO NO NO.
Absolutely not.
Has nothing to do with burning anything out.
First, you will not get 2SS rates because you only have 1 antenna connected, so you're wasting half your potential performance.
Second, because MIMO radios are TX from both chains and splitting half the power on each, doing that reduces your SNR by 3dB, your cell radius by 33%, and the total area of your cell by 50%.
Third, you also eliminate the 2nd RX chain for MRC which will make it difficult to maintain a given rate at a given range.
It's called "Multiple In Multiple Out" for a reason.
There is no cost penalty for connecting both antennas because we sell only MIMO antennas that include two elements for the same price as we used to sell single element SISO antennas. Even our omni kits have two antennas in them.