The almost universal view is that we are in a recession. It's clear that people have already lost their jobs, whilst others have lost chunks of their income. The idea that things will bounce back to where they were is on the unrealistic side of optimistic.
Recession means reduced demand, and that means overcapacity. Shrinking a business successfully is a very difficult thing, and many otherwise good businesses will fail, adding to the woe.
As Southend is the most marginal of the London-area airports, I would expect it to suffer sooner than the others. The Wizzair operation is unlikely to last in the long-term, and you can be sure that Ryanair will use the situation to reduce its costs - that could affect SEN, STN, LTN and/or LGW.
I don't see an influx of newly formed airlines, but we could see overseas operators opening new London services to any of the London-area airports.