How can anyone pass an exam without sitting it? I can see how Universities may want results, but when I want to University I was given an entrance exam, it was made very plain the maths required for engineers is complex, and they did two engineering degrees, one where the maths was taught from scratch and one where it was assumed you knew the basic 'A' level stuff. So for University it is no problem having no 'A' level, any 'A' level student will have 'AS' anyway so why even try to guess result for University.
More to the point is employers, they want some school leaving certificate, and OK for a couple of years they will remember students could not take the exam, but in 5 years time there may be a job which needs 'A' level and this years students will not have a valid certificate, even more so with the 'O' level or think combined with 'CSE' now, so what is needed is a exam which does not need to be before September but does need to be available so students can show it to employers in the years to come.
Some could be random selected questions with an on line exam, but the same random generated papers could be produced for written exam, and if random then it does not matter if students talk about the questions, as they will vary, so there is no reason why schools should not open in the evening to conduct exams.
There are some exams where physical work is involved, art 'A' level for example, but the art 'A' level was a 12 hour exam taken over a week, so no difference to normal allowing students to take it in free time.
So in real terms only problem is schools and collages will need to test students without knowing the chances of passing so their score may drop, so simple scrap the scoring for two years so students can return and take just the exam.