Hello @evox ,
So like below the ring topology is connected:

You are good to shutdown SW2 & Sw3. If you are shutting down interfaces on SW2 and SW3 which are the part of IRF then you have to console access the SW2 and SW3 and manually shutdown the interfaces connecting to IRF else remove the IRF cable.
[SW1]dis irf topology
Topology Info
-------------------------------------------------------------------------
IRF-Port1 IRF-Port2
MemberID Link neighbor Link neighbor Belong To
1 UP 2 UP 4 309d-1669-0100
2 UP 3 UP 1 309d-1669-0100
3 UP 4 UP 2 309d-1669-0100
4 UP 1 UP 3 309d-1669-0100
[SW1-Ten-GigabitEthernet3/0/49]sh
Operation not supported on the last active physical port bound to IRF port which connected to the master!Please shutdown the other end of the link.
[SW1]dis irf
MemberID Role Priority CPU-Mac Description
*+1 Master 32 309d-1669-0100 ---
4 Standby 1 309d-2117-0400 ---
--------------------------------------------------
* indicates the device is the master.
Thanks!