Germany's minister of health said this week that "parties and funfairs" will not be happening for a long time. This puts serious doubts on this years Oktoberfest.
Also the NZZ had an article on travel after Corona and its noted there that international travel is highly unlikely this year. It "might" be possible again next year but only if there is a medication or a vaccine. Source (German):
https://www.nzz.ch/reisen/corona-tourismus-experte-zum-reisen-in-zeiten-des-virus-ld.1549850
Oktoberfest will really struggle to go ahead. It relies on visitors coming from all over the world. I went last year and met people from France, Australia, Brazil, USA, so many other countries and then of course a lot of German locals are there too. Not to mention as well at Oktoberfest there are millions of people and the beer tents are relatively cramped spaces, with thousands of people inside each one, with close human contact and people sharing beer tankards etc. I really don't think it stands a chance this year at all unfortunately.
A lot of the German fairs are also similar to Oktoberfest in the sense that they are huge "parties" where all the locals dress up, gather and drink in massive beer halls. I did Düsseldorf, Bremen and Oktoberfest last year and they are all similar really; the rides are only one aspect of the fair. That's why letting any German fairs go ahead will be a massive push as they are essentially the same as letting festivals go ahead. UK funfairs( bar potentially Nottingham and hull and WW) tend to be on a much more remote and local scale, so the chances of them being able to re-operate this season are higher.
Nevertheless, the chances of the parks themselves opening this year are significantly higher than the fairs being able to operate, as in the parks I think it is easier to enforce social distancing measures, better standards of hygiene and cleanliness etc. However, if international travel is potentially written off for the whole year then I question the worth of some of the bigger parks even opening, for example:
Phantasialand, whilst most visitors are mainly German, does also rely on dutch and English visitors to generate income (PHL is a very popular destination for English school trips and scout groups).
Europa Park, has a significant amount of its workforce coming from France, who may well not be able to get to work. EP is also significantly relies on international visitors, from France, Switzerland, Russia and England.
Disneyland Paris relies heavily on international visitors, especially from the UK and also from other countries such as Germany.
Other parks such as Portaventura and Efteling also rely a lot on international guests to increase revenue.
That's just looking on a European scale, obviously Disney Orlando resort is heavily reliant on international visitors as well and people come from all over the world to visit the Disney and universal resorts in America. If international travel is off the cards for the whole year, then it really questions whether it is "worth" the parks even trying to reopen.
A lot of the parks on a more local scale, for example a lot of the more local based UK parks(Drayton, Thorpe, Chessington) and European parks (such as tusenfryd, sarkanniemi, linnanmaki) mainly generate revenue from locals, and therefore from a business perspective, if possible, it would be more worthwhile to open these parks, albeit with measures in place, as the loss in revenue isn't going to be so great as if you rely heavily on international visitors.