My short answer would be NO!
The long answer, so you have some information for your boss:
Let’s do some maths…
At present, in some parts of the country the case rate is 1500 cases in 100000. So that works out as around 1.5% of the population has COVID at any one time. (Data from the gov.uk website, I have no idea where you live, but the case rate is soaring all over the country)
At a party with 200 guests, you could expect to have around 3 positive cases (give or take, and at this particular moment in time). Many, especially now with vaccinations, are asymptomatic, but may still transmit the virus.
Now, in a poorly unventilated indoor space you can expect transmission to be pretty high (and that is without alcohol, and the lack of masks and social distancing) - the delta variant is especially transmissible in these circumstances - just look at the data coming out of The Netherlands who opened their night clubs and dropped many public health measures on the 26 Jul. In the week following, the case rate rose 800%! Today the Prime Minister of The Netherlands apologized to his country for opening up too soon, and has reinstated public health measures. When he opened up his country, there were just 558 cases a day (Statista.com), and the case rate had been low and steady for some time. They are also vaccinating at speed.
So, taking that all into account, you can expect the virus to be present and able to transmit - so the only question is how many people contract it that evening.
Today, Jeremy Hunt stated in the Commons that 1 in 40 people that contract Covid will need hospital care. This is despite vaccinations (although much lower rate than before the vaccine).
So, if just 40 people contracted Covid from the party, you should expect one guest requiring hospital care. But how many could become infected?
Now, some of these figures will be a gross underestimation by the time we get to the end of July. At this point in previous waves we have always locked down. We literally have no idea how high cases will climb before we peak (through infection derived herd immunity or self imposed lockdown due to fear).