Don't close the front panel, just hide it using a Property Node of the VI (Front Panel Window->State). If you close all of the front panels, your application stops running. So hide it instead.
There are only two ways to tell somebody thanks: Kudos and Marked Solutions Unofficial Forum Rules and Guidelines "Not that we are sufficient in ourselves to claim anything as coming from us, but our sufficiency is from God" - 2 Corinthians 3:5
You might be looking for "dynamically starting a VI". A would dynamically start B, and can then safely quit. Note that B needs an open panel or an explicitly opened reference to itself, or it will stop running.