Whether low-priority tasks will receive messages and execute them depends on the specific scheduling algorithm and how the program is written, such as whether the priority is real-time or based on time slices, whether message sending is blocking or non-blocking, etc.
As for whether a deadlock occurs, it should be definitely not a deadlock. Because the condition for a deadlock to occur must be that both tasks are waiting for each other, and if the high-priority task is blocked after sending a message, the low-priority task will definitely be scheduled for execution, and there will be no waiting for each other.