Yes they do, I know a Talib of Sheikh Nuh who left the tariqa to become a Qadri. He sought permission first, because our area has no other shadhilis, and the only sufis in the area were Qadris, Sheikh Nuh gave his blessing to join up with the Qadris. Later on the brother missed his sheikh very much and asked Sheikh Nuh personnaly to accept him back, which Sheikh Nuh graciously did. ...And in our tarriqa, permission should be sought for leaving or changing a Tarriqa, To leave or change without permission would be conssidered an insult to your Sheikh