Complex sentence: The PSCU seems to have disappeared after this time, and Poulin and his supporters seem to have joined the re-united Social Credit Party of Canada under Caouette's leadership in 1971 or thereafter.
Split into simpler sentences: The PSCU seems to have disappeared after this time. It is possible that Poulin and his supporters joined the re-united Social Credit Party of Canada under Caouette's leadership in 1971 or thereafter.