Request for Assurance applied

[mabhang]

Hello all,

I have a query regarding my parents visitor visa and below are some details.

They travelled to the UK on visitor visa on 17th April. Their visa expires on 1st July. We had their tickets booked on 28th June for the return -> Manchester to London; London to Bombay. Now with the situation in India, we were really worried for their travel back so we did a 'Request for Assurance' on compassionate grounds (mentioning health issues and all) around mid June. But few days after we did the extension application, British Airways emailed saying their 28th June flight, London to Bombay has been cancelled. However they have rebooked on 29th June same flight. But the flight from Manchester to London remained the same i.e. on 28th.
We called BA, asked them if they have a flight on 29th from Manchester to London but they had none. neither did they have any other date before the 1st of July matching the same dates for both flights. All other flights were 2k+. All normal flights can be seen from 19th July onwards.
So now we are confused as hell and called Coronavirus immigration team for advice. They said that you should leave if there are flights, else you can apply for assurance, based on the flight changes and that you wouldn't be seen as overstayer.
So we did. We got a bit confident based on the immigration call, hence we also changed their flights for after 19th July.
Just when we changed flights, we got a reply for the first request of assurance (compassionate grounds one) saying they have rejected as there is sufficient time to leave and the request of assurance is only for whose visa expires between 1st Jan and 30th June. They cannot grant assurance as our visa expires after 30th June and that we should keep an eye on the gov website for updates.
So we called the immigration team again and they said the same thing (make an application, wont be seen as overstayer). we also asked if the assurance is rejected, what will happen? they said we will get a grace period to leave.
My question is what to do? should we wait for their decision, or rebook the London to Mumbai flight on 29th and go to London by car (so inconvenient). The biggest thing we are scared about is being looked at as an overstayer!
Please help

PS. Sorry for the essay!