I have sent emails to CIH@homeofffice.gov.uk and tried calling on paid and other numbers and also paid email service. I only got one response from CIH of of two replied later. When asked if vignette validity will be automatically extension for outside UK. The reply I got was like post office will ...

My husband and I are in a similar situation. Our vignette expires on April 24th. With the current lockdown in India, there is no clarity if international flights will be allowed. I have also written to the home office but have not received a response yet.