I'm not british, but I hope people will vote to stay in Europe.
I don't think that Britain or the EU will collapse if the UK leaves, but I do think it will weaken both.
Here are my thoughts on why the UK should stay:
The EU is a big market. The EU without the UK is a smaller yet still a big market. The UK outside of the EU is a much smaller market. Who do you think has the better chances in negotiations with the two biggest worldwide competing markets (China and the USA), the EU with the UK, the EU without the UK or just the UK? It's also likely that the banking sector in London will shrink considerably, as the UK as a market has become less attractive.
2. Less influence
Just by leaving the EU doesn't mean you'll have a bigger voice in the world, a bigger voice in world wide economics or even local economics. The UK will most likely stil be forced to live by rules set up by the EU, the USA or China. Inside the EU the UK at least can influence what the EU is trying to do. Look at Norway, they aren't in the EU and still have to abide to rules set by the EU without having any say.
3. The EU needs a UK that is commited to the idea of the EU
Lets face it, the UK so far was never really convinced of the project, at least not to the extent that Germany and France are/were. The UK only wanted to join the EU for economic benefits, and because the UK is part of Europe, and the EU wants a united Europe, they were willing to allow the UK to cherry pick what they wanted so the UK would join. This has led to the UK never feeling like they really belonged in the EU (eventhough, imo they do).
As long as it was smooth sailing the UK was willing to put up with it.
But now that it's rough sailing, and the EU is having one crisis after another (Greece, Ukraine leading to a trade/propaganda war with Russia, refugee crisis), and the use of the EU as a scapegoat for national deficiencies has become popular, leading to the rise of nationalist parties, this feeling of not belonging leads to the feeling of needing to leave.
I really hope the UK will vote yes and then show more commitment to the European idea and help find the right direction for the EU. The UK and the EU has more to gain if they work together.
Platforms: Wii U, New 3DS, PS4, PC
-Yoshi's Wooly World
-Fire Emblem Fates
Zone: Europe (Germany)