emanuel,

I will try to answer your questions;
NGL’s (Natural Gas Liquids) are extracted from the natural gas flow to meet transport (pipeline) and sales gas specifications. This is both to avoid liquid fall out (due to changes in pressure and temperature) and to ensure as good combustion as possible at the burner tip.
After NGLs are extracted (separated) the Nat Gas and the NGL’s are sold separately.

1) NGLs are ethane (C2), propane (C3), butanes (C4), pentane (C5) and perhaps come C6.
During standard atmospheric conditions ethane, propane and butane are gaseous and normally kept in liquid form under pressure.
LNG (Liquefied Natural Gas) is methane (C1) cooled down to approx. minus 163 centigrade for liquefaction and transport to the market.

2) This depends on your customer/market, but normally NGL’s are extracted and sold separately.

3) What you refer to is called “Shrinkage”, that is as NGLs are removed from the feed the total volume of Nat Gas is reduced at the outlet. The “shrinkage” is dependent of the composition of the feed, but roughly it takes 250 Scm (Standard cubic meters) of C2, C3, C4 in gaseous form to make 1 Scm of NGLs in liquid form.
To answer your question more directly you may normally expect to lose anything from 0 - 10 % of your volumetric gaseous feed during extraction.

4) Normally all Nat Gas is processed to extract liquid components. There are exceptions where a richer feed is mixed untreated with a leaner feed as long the resulting mixture meets transport and buyers specifications.

5) No, the extraction process does not reduce the total amount of Nat Gas made available to the market (except from fuel used in the extraction process). The extraction process just splits the components into gaseous (Nat Gas) and liquid (NGL) states.

I hope the above clarifies a little.