That's up to Felicity.

She pushed him out so she could seize his family asset's which belonged to QC likely due to tax incentives and such, then they depreciated the value of QC stock to try and bankrupt the family.
But Oliver still owned 50% of the stock, so he should even after Ray brought the remained of the company he couldn't force Oliver out of his 50% so either Oliver owns 50% of PT, maybe 25% if PT & QC was a merger and not just Ray renaming QC, so either Oliver should own 25-50% of the company still, right?
I mean why else was he broke? because even if he sold his stock when Ray brought it he'd be minted, makes no sense to me it really doesn't.

He'll have to get it back to merge with Wayne Enterprise

When Summer Glau decides to yield up her lion's share of the stock she was trying to get a majority share of in season 2. Oliver plus Walter just nosed her out each time, until the nitwit signed her in as temporary CEO, from which position she could wangle him out of there.
Still, firing the CEO does not deprive him of the stocks he owns so I still don't know what that was all about. Maybe there was something very off in his CEO contract. Maybe Walter had the hots for Gospozha Rochevna, and used his stock Oh, never mind.

Because supporting your thesis is tough, but throwing adjectives is easy.