Any short route train (overnight ones) with one side journey time less than 10 hours, can still be rescheduled as the resulting rescheduling chain won't last long.
Cancellation of longer route trains should be done if the delay is equal to/or more than the difference of resting time at destination station and minimum time required for primary maintenance. e.g. 14055/56 BP Mail rests at Dibrugarh for 19 hours. Considering that CDO Dibrugarh will require 6 hours for maintenance of BP Mail, the maximum delay that should be allowed for BP Mail from Delhi, should be 19-6=13 hours. Moreover, average delay of train can also be included here.
I...
more... think a good solution for IR is to have standard rake composition for different type of trains. I mean superfast trains can have a standard 24 rake composition with fixed number of AC, Sleeper and General Coaches in all trains. Same for Shatabdi and Rajdhani type trains. By doing this, delay of trains can be reduced as Railways can keep buffer rake(say X) to be used for one train(say 1 UP), and then the rake of corresponding link train(1 Down) can be used for other train (say 2 UP).