“I believe that’s already the case.”
Yes, it would seem that would apply directly to the reasonable fear for imminent death or bodily harm part. If you left and came back later the prosecution should be able to argue your reaonable fear left with you.
I agree with the other poster to an extent who was concerned about that provision incriminating homeowners who go to the bedroom to get their gun, etc., but I don't think it applies because SYG per se is pretty much for use in public as I understand it. Self defense in your own home or business was always legal and the new provisions of SYG aren't required in those cases. In any case, if the law is restricted in that way, I'd have no problem with some explicit verbiage being added to make it clear those cases aren't the ones to which it applies.