unavailability of IT staff scenarios

We are trying to come up with some table top exercises for testing staff continuity levels in regards to an internal IT support section who support the IT/Network Infrastructure for a fairly large organization >2500 employees (e.g. ability to manage the risk of losing members of the support staff team short/long term), documenting the various scenarios around IT support staff availability (or lack thereof), and coming up with solution to manage/minimize the impact on the section and service delivery. 
We have made a start, can you think of any more scenarios whereby you could be down in numbers of your available resources with limited pre-warning. It doesn’t really matter which teams within your traditional IT section it relates too, e.g. DBA section, Infrastructure/Network team, end user/desktop support etc:

The initial risk scenarios that have been identified so far are:

1. Staff short/long term illness affecting individual staff members availability. General unplanned absence (no/limited pre-warning, unlike things like maternity leave, retirement which can be better planned for etc)
2. Major flu pandemic and possible short or long term absence to a significant number of staff at the same time
3. Staff leaving the company for a new job at another company, and failing or struggling to re-recruit in key positions
4. Adverse weather conditions (inability to access main office etc)

I have a feeling we may have missed some other scenarios, so any thoughts on others would be welcome. Scenarios with possible solutions to manage the risk also welcome so they can be factored into discussions.