Happened to me on an Austrian flight as part of a United ticket. Flight canceled, rebooked on LH, and got an extra 1000 PQP, which helped my requalification for 1K that year. And if the PQPs are lower than the original flights(s) with an involuntary rebooking, you can always request original routing credit (ORC). I appreciate there are still some silver linings with IRROPs.