Pictured here is what backwardation has looked like (red channels) and how it is likely to unfold now (orange tick channels).
The channels you see are drawn around UVXY/VIX. The fact that UVXY normally loses value over time is due to contango in the VIX markets. In times of crisis, the VIX go into backwardation (where the price for a short term contract on something is higher than the long term price).
When backwardation occurs, UVXY starts gaining value every day relative to the VIX . The chart shows a period last January where UVXY did just that. If Brexit works out as the same sort of crisis, we can expect the current UVXY/VIX ratio to move from .6 today up to .8 in 4 weeks. From there a bottom should be found and the normal contango structure (with UVXY price decay) resumes.
How to play it? You can buy the dips on UVXY and calculate targets based on the VIX top you expect * the ratio for the day on the chart. You can also use the same technique to judge which strikes to pick on buying UVXY calls. Same goes for selling puts - find a price likely to expire out of the money and collect premium. VIX derivative premiums will appear obscenely high ... use the ratios and prior VIX spike paths to calculate good strikes and values.
The indicator on the bottom simulates the UVXY roll trade - the black line is the average of short term prices and the red is the average of the midterm, offset by 30 days. When the black is over the red then the options that are sold by Proshares that day are sold at a profit (for more than they cost when they were midterm ).
Keep a cool head - comes and goes. Do the math and understand the structure and you can make money in either direction.