Do we need to have a dedicated QA in development team and what happens if we do not have dedicated QA?
Having someone specialized in single role doesn’t matter if it is QA or any other increases the risk of bottlenecks. There is the danger that some area of project knowledge is concentrated on one person which makes it harder to optimize team as a whole. I have often seen that tester will sort of start living in a world of his own with his special tools and reports and stuff that nobody else has the time to immerse into (see more here). In a way that is of course also good because that provides additional independent view of the system.
What will happen if there is no dedicated tester? First, developers will be very eager to automate as much testing as possible. That means not only more unit testing but automation on functional and system testing levels (actually the latter will often result in less unit testing). We all know that automation of tedious, repetitive tasks is good so what do we actually loose if there is no dedicated QA?
I think that main thing that is hard to compensate is that different view of the system. I mean any developer can learn the tools and theories of QA and indeed should learn but there is always a difference in results when doing explorative testing for fun and doing it because you have to.
Ürgo Ringo's blob 
I like the idea of every team member being able to do a little of everything, but I don’t think this means that we shouldn’t have people who are more specialised in particular areas.
I believe having dedicated QAs is very good, since they will be the ones with the greatest knowledge around coming up with specific testing scenarios, exploratory testing, possible defects metrics and so on. But having developers helping in the QA phase is a very good thing specially if the QA team becomes a bottleneck.
Also I think that ideally QAs should have automation knowledge, to help in deciding what acceptance criterias are worth automating and what not, to pair with devs in ACs automation but also automating specific test scenarios after a story is dev complete. This helps in keeping QAs from isolating themselves in their QA world.
It seems to me that in the context of test automation the requirements for a good tester are quite similar to the requirements of a developer. So much so that it probably makes sense to consider such tester as just another specialisation of developer same way as we have database developers, UI developers etc.
In this case the argument for dedicated QA would not differ much from argument for or against dedicated DB quy. Yes, in big team or project with above average complexity in database design you will benefit from such specialist. In smaller project you may find that you simply cannot afford to have database guru and having less tuned database is OK as long as it doesn’t start causing real performance problems.
In practice I still see a lot of projects where functional test automation is not done. So lack of dedicated tester alone is certainly not enough strong force to push every team to higher test automation.
In these projects there is still need for dedicated testers who are among other things able to deal with repetitive tasks. In some cases this allows to reduce the costs of development in other cases it will do so only in the short run.