Post L) mastectomy.

I was in hospital for four days and left without a drain (I had two). While I had quite definitely stopped leaking fluid (and healed quickly and effectively, with excellent arm mobility), I did develop a persistent seroma some time later, which defied aspirations (I had several) and utimately led to an infection (all those excellent nutrients unfortunately feed bad bacteria that we all have in our bodies). However this is unusual. 

But how long you may need drains depends on your own body and your surgeon's preferences - be guided by the specialists. Best wishes for a speedy recovery.