I have on two occasions asked them to close my flight plan which they were quite happy to do.
I would be interested to know how they would close your FPL. This is not done in the UK. Your FPL is pending (or inactive) until such a time as a DEP is sent. If you do not arrive by DEP + elapsed time + then ATSU (or your designated responsible person) should initiate alerting action if they notice. If no DEP is sent, no alerting action can be expected. This is quite worrying for IFR to VFR and IFR leaving CAS, which do not genereally have departure messages sent.