If Improvised Arsenal leaves the battlefield before its second ability resolves, the token will still enter as a copy of Improvised Arsenal, using Improvised Arsenal's copiable values from when it was last on the battlefield.

The token doesn't copy whether Improvised Arsenal is tapped or untapped, whether it has any counters on it or Auras attached to it, or any non-copy effects that have changed its types, color, and so on.

The token copy will have Improvised Arsenal's abilities and will be able to create copies of itself.

In the unusual case where Improvised Arsenal becomes a copy of something else while its second ability is on the stack but before it resolves, the token will enter as a copy of whatever Improvised Arsenal is copying. (This is the rules equivalent of "yes, and.")