I don’t think there would have been a 2017 or 2019 election. 2020’s would be around the start of Covid, which could make things tricky.
Depends, given that the government could've always just sought a special Act of Parliament extending the maximum duration of the 56th Parliament by an extra year beyond its 5 & postponing the election 'til 2021 like they did with all of the local elections, just as the 1910 Parliament was prolonged following the outbreak of WW1 & as the 1935 Parliament was prolonged for a total of 10 years all the way 'til 1945 due to WW2. Although the Lords would actually be entitled to a full-on veto here, whether they'd be willing to use it at the onset of a pandemic that was still novel at that time 12-14 months ago is another matter.