C4 has already hired BBC independent commissioning group head of drama Tessa Ross to replace him, but a joining date has yet to be confirmed.
C4 executives are now trying to speed up her arrival, but there is concern among indies that drama commissioning will be in limbo until she joins.
A C4 spokesman said that commissions will go ahead as planned, but new drama proposals will not get an answer until Ross is officially on board.
Neal and McKenzie, who originally said they would go at the end of the year, will probably leave in September or October, along with Young.
Neal is believed to have arranged a development deal with C4 and sources said he already has at least one high-profile writer on board. Although neither he nor Young would comment, Young's soap experience suggests Neal feels confident about the new indie producing a long-running serial.
Young joined C4 just a year ago with a specific remit to oversee Brookside and Hollyoaks (Broadcast, 4.6.99). At the time the soaps' creator, Mersey TV director Phil Redmond, described him as 'one of the best appointments C4 has made in years'.
Young started out as a location manager on EastEnders.