Cancelling and Sickness
Please always try to book accommodation or tickets with a flexible or refundable/rebooking option. The university is unlikely to pay for travels that have not taken place.
Should you have to cancel the travel due to illness, and if the travel was approved, you can apply for reimbursement of the preparation expenses. Note that it is your responsibility to keep the expenses as low as possible and provide proof of sickness, accident, or otherwise - ask for cancellation or reimbursement with the airline/booking providers first.
If you get sick or have an accident during business travel and need to come back earlier, some of your expenses can be reimbursed, if the travel was necessary and was approved by the department earlier. The university accident insurance only ensures employees and only for short trips. Students and external parties should take out insurance of their own.
To make sure you are safe, it is best to take out health (accident) insurance for travels before the travels (about 10 EUR annually with any German insurance provider - Reisekostenversicherung). The insurance provider will pay most of the expenses much more easily and will also ensure your safe transport back home.
If you want to be sure to get your money back when cancelling non-refundable things, take out cancellation insurance (Reiserücktrittskostenversicherung). Some travel insurance packages come with this as well. Also, try to always book accommodation or flights with a cancellation option.