If this happens in flight, there is no restriction in FL. FL250 is only MEL and so applies in dispatch.
the main reason to close the bleed is to avoid having one wing anti iced and the other one not. Just in case you would not see that you are picking ice on the wing, with one wing being antiice and the other one not. that could result in an unexplained roll .... ;-)
Of course that scenario is not a problem when above FL300 where picking ice remotely is rare.
The other reason is to avoid having a bleed trip off on the side where the wing anti ice is on at high altitude.