We have been in this situation twice on sits . The uncertainty in this situation is stressful as you wait to find out how the host is , continue to care for the pets and at the same time co-ordinate plans for your own accommodation / return home if the sit ends early . Whilst not knowing exactly when the sit will end …it’s also possible that the hosts maybe away longer depending on the recovery time and if they will be permitted to fly home …… if they need to be medi vac home that also takes sometime for insurance companies to arrange . 
If the sit is curtailed , will you need alternative accommodation ? You can start researching your options now ( hotel , AirBnB another sit ) incase you might need it . Then you will have a back up plan ready, if it’s required.
The THS Urgent Support number is on your dashboard. They can end your current sit date when that has been confirmed by the host ( get it in writing-eg screenshot of a text ) . This will enable you to apply for other sits . They can also explain the process for claiming under the sit cancellation plan ( only applies if you are a Premium Member )
This thread gives advice about how to make a claim for alternative accommodation.
https://forum.trustedhousesitters.com/t/tried-tested-process-for-premium-insurance-claim