If there was a piece of foreign material blocking it, or if the bypass valve is shimmed too much, thus preventing the bypass plunger from opening, the consequence would be unlimited high end pressure. It can reach the point of potentially popping the crimped seal on even a High Performance
oil filter such as FL-1HP. I have had this happen, it's exciting and makes a BIG mess. POW!
However too answer your question, YES you would have pressue but it would be very unstable even though the gauge may indicate otherwise. It is like a huge internal leak. It may also tend to aireate the
oil considerably. Fix it.