Can a pit in the nasal bone regrow or can it be closed?

Hello and thanks for the question.  It is difficult to ascertain exactly what the issue is from without examination. It is not unusual to have minor irregularities after removal of a hump from the bridge of the nose; however a true pit is not common.  I recommend discussing the issue with your surgeon. 5 months is still relatively early in the recovery period so the issue may slowly improve. 

This sounds like an unusual issue. The fact that it is not visible except when inhaling reflects the negative pressure you generate when breathing inwards. There is a chance this will heal over time, but it also could become worse as the swelling in the tissue goes down over time. You need to watch this closely with your surgeon and follow it for at least a year. If it does not resolve then a cartilage graft or similar repair may be needed. 

It sounds like a little too much bone was removed from the upper bridge of the nose, which can result in a depression or indentation in this area. It is unlikely that the bone will regrow and replace that which is missing. It takes about a year for all swelling to resolve and it will be wise to wait that period of time before considering treating it. This type of depression can be improved by filling it with crushed cartilage or certain fillers.