Leaving Characters

Before coming here I did look in my copy of the main rulebook for an answer but couldn't find anything about characters leaving and joining squads , so here is my question:

Can I deepstrike my Archon via webway portal with his unit of blasterborn, have the Archon leave the unit using a Run move, then have the Blasterborn shoot and (hopefully) kill a unit so that both the Archon and the Blasterborn can make a soulburst move (Assuming they are taken as part of a 7 unit or more Reborn Warhost detachment) ?

The answer would be 'no' right? Because characters have to leave a unit in the movement phase and that is impossible for my deepstriking unit, yes?

Many thanks in advance,

No, not in the way you described. Joining or leaving a unit may only be done in the movement phase. That said, if you deep strike them embarked on a transport, then disembark them and announce that your archon is leaving the unit when they disembark, I'm pretty sure that is a legal maneuver.

Or by not disembarking the Archon, but yes I concur that this is correct.

To be specific, under the INDEPENDENT CHARACTER Special rule:

"In order to join a unit, an Independent Character simply has to move so that he is within the 2" unit coherency distance of a friendly unit at the end of their Movement phase."