What can happen to a project when a key employee suddenly quits or is forced to go on short-term disability?

Read the case scenario and then please write 1-2 paragraphs responding the following questions using APA formatting. Please submit your assignment to your instructor.
Planning for the Unexpected
Unexpected situations happen all the time, and the more you plan for them, the better prepared you’ll be when developing software. Your employees will get into accidents, contract viruses, and diseases, and experience other life issues. These scenarios lead to unplanned absenteeism, which can throw your project plan into a tailspin. What can happen to a project when a key employee suddenly quits or is forced to go on short-term disability? When reviewing all the different SDLC methodologies, which one offers the greatest flexibility for unplanned employee downtime? If you could choose when your employee was absent, which phase in the SDLC would be the safest for your project to continue and achieve success? What can you do to ensure that you are preparing for unplanned absenteeism on your project plan?