It's of course important to ensure that the combined package of A+B is more attractive to miners than the C transaction. The extra weight of the embedded transactions in C helps with this. Also it is worth noting that the fees for C will never be paid because it has been replaced. Thus there are no extra costs for using this package relay scheme, unless perhaps the weight of A+B is very low and B needs to pay a higher fee rate than necessary to ensure replacement of C.
If not all miners adopt this incentive-compatible replacement, there's a chance transaction C ends up being mined. This is likely less probable if the fee rate for C is kept to a minimum. If transaction C is indeed mined, the operation can be retried with a modified B and C, though the fees paid for the initial transaction C would be forfeited.
Joost