The product of a monthly hour guarantee and your hourly rate yields a minimum salary level that you can depend on, regardless of schedules. Most US airlines use this system.
Many schemes are used in the details, so one person cannot describe how sick days and mechanical delays are "always" handled. One scheme is:
A sick day is paid at a standard level which is the number of guaranteed hours divided by the number of minimum obligated work days (e.g., 75 hours guarantee / 20 days minimum = 3.75 hours pay).
Each trip segment is paid at the patterned/scheduled time or the actual time, whichever is greater.
If a trip is cancelled due to a mechanical problem, and a replacement trip is not flown, a set number of hours are paid.