The most impotant thing to understand about bicarbonate is that it is alkaline (i.e. is a base). As such it tends to pull pH higher in the mash than we generally want. The brewers main job when it comes to brewing water management is to get rid of that alkalinity one way or another. Some of the ways are dilute it down until it is insignificant, try to get it to precipitate as chalk or try to drive it off as CO2 (by adding acid either mineral, organic, acid from dark or sauermalz or acid generated when calcium reacts with malt phosphate). Once the pH is in the proper range (5.2 - 5.4) the bicarbonate is essentially gone. At pH 8.3 98% of the carbo species ions are bicarbonate, at pH 7 that goes down to 80.5%, at pH 5.4 it's 9.5% and at pH 5.2, it's 6%. That doesn't mean 6% of what was originally in the water. It's means 6% of whatever is left after the acidification process converts most of it to carbonic. Thus, in the normal course of brewing, you must remove most of the bicarbonate. The fact that you got proper mash pH says that you did.
Finished beer will be, typically, at a pH of 3.5 or so and carbonated to sround 2 volumes. At pH 3.5 only 2.3% of the total carbo is as bicarbonate but there is a lot of carbo as carbonic so the bicarbonate content would be around 65 mg/L until you pop the top at which time carbon dioxide rapidly escapes and bicarbonate starts to convert to carbonic to re-establish equilibrium (but at much lower levels).
It's hard to answer such questions precisely as the only tool available is thermodynamics which gives answers at equilibrium and it takes a freshly opened bottle of beer a looong time to reach equilibrium.
