I do not know anything about the lifespan of SIP's but 50 years sounds about right. I have never used them and if I can help it never will.
It is certainly a quick and easy way to enclose a frame. And for most frames I have seen they are also necessary since I doubt that a 4' knee brace on a 8' or longer post is hardly enough to stiffen any timber frame sufficiently.
Why are they being used instead of proven methods hundreds of years ago? My guess is the cost and speed of assembling a frame/house. It also protects the frame as compared to a German style frame with exposed timbers which needs some care to maintain its beauty.
As to glue degrading when getting wet. Why or how would the panels get wet after installation and being covered with exterior wall covering? If built right they should never get wet other than under occasional high humidity levels. But then they will dry out again. That is if the installation was done correctly.
