I've moved this from Edge Code to the Edge Animate forum, since I think that's the tool your question pertains to.
You're hitting a race condition right now. The deletion will not wait for the animation to play. Instead, you're probably better off not using beforeDeletion and instead setting up a trigger in the symbol to delete itself, then call a label that will play that selection.
Hope that helps,
I skirted the situation by putting on stage method deletes the object that the call to
sym.getSymbol ("SimbolName"). playReverse (500, true);
I put a symbol on the timeline trigger position 0
sym.getParentSymbol (). getSymbol (sym.getSymbolElement ()). deleteSymbol ();
It works perfectly, however I think a workaround.
I forgot this,
The Symbols must be false as autoplay timeline, in creationComplete (symbol method), i call sym.play (0, false), not to run the deletion trigger in position 0 in play moment.