when i create a note (e.g. C4) and extend it 6 measures, you can clearly hear the note decaying and is mostly gone by the end of 6 measures. just as if i plucked the note on my personal Fender Precision (which has a number of mods like badass bridge and updated tuners etc) which sustains the notes for a long time (longer than the EZBass does… 
) (by design) so if your EZBass instrument is not decaying, then must be a setting which causes it – examples may be you’re using it in a DAW and have a compressor / expander causing it to elevate volume, an automation control, etc otherwise i’m not able to reproduce a situation where the notes are not decaying.
in my experience (as a long time pro bass player), the modern and vintage instruments seem to operate as expected.
Glenn
www.runnel.com
www.reverbnation.com/fossile
the default “modern” and “vintage” basses mimic real life – so notes decay i think if you got an synth bass, then having the notes sustain as long as desired would work. and in your DAW, you could have 2 basses – one “natural” for the initial transients and tone, and a synth to sustain. (not unlike the old days of record with a double bass for sustain (plucked and bowed) and depth and an electric bass for transient and clarity – e.g. wrecking crew)
Glenn
www.runnel.com
www.reverbnation.com/fossile