edit : Haunebu already posted a relevant article (10 double header)
10 double headers and 11 other days mean a total of 21 days. I guess if they could finish the tournament in three weeks, then the T20 World Cup can proceed as planned. But the catch here is that if the world cup is to be played in India, then it takes additional time to set up the bio-secure bubbles and to quarantine the players who are returning from UAE. So the best option here would be to stage both the tournaments in the same country. Also, the BCCI team (Shah, Ganguly.etc) are in Dubai right now, and the rumors are that they are exploring the option to stage the world cup in UAE.