Apologies, so the ticket is from Manchester to Frankfurt on LH, connecting to Muscat on Oman and Manilla on Oman. The initial outbound has a one and a half hour transit time which is fine. I was thinking of these 2 sencarios and wondered if EU261 would be payable;
1) LH is delayed on the MAN to FRA sector by an hour meaning I am less then MCT as I need to change terminals I dont get to the gate on time so they rebook me on another carrier lets say EK which an hour later but still gets me to Manila an hour later then my original flight time or an hour later since EK has a 1 hour stop in DXB which is viable compared to Muscat which had a 3 1/2 transit time.
2) On the day the flight goes tec at Manchester or for some reason its cancelled. EK/QR fly later the same day and assuming they have seats, they also connect and arrive at a similar time to my original arrival time, just a shorter stop at each airport. If LH cancelled this flight but LH were able to rebook me to arrive at Manila within a similar time span, would they still be on the hook for the cancelled flight even though I arrived at a similar time.

The shortest flight schedules for this route are 18 hours and I am booked on one with 21 hours so I could relax a little on the way but if LH cancelled the first flight, there is scope to recover