ILR-LR and PBS Dep. visa validity.

Hi Guys.

I just want to know please that If someone get his ILR on Long Residency basis. His dependent is Tier 1 PBS Dep and her visa is still valid for another 2 years. What if she don't switch to FLR(M) until the expiry of her visa. ?
I want to know whether her visa will still be valid until her visa expire and she can travel and come back on the same visa and she can continue living on the same visa for another 2 years after her husband gets ILR on LR basis.

Thanks