What's needed, alongside an evacuation plan, is a realistic program to stabilize conditions for those left behind.
( ( What ( 's ( ( ( needed , ) ( alongside ( an ( evacuation plan ) ) ) ) , ) ) ) ( ( is ( a ( realistic ( program ( to ( ( stabilize conditions ) ( for ( those ( left behind ) ) ) ) ) ) ) ) ) . ) )
(ROOT (S (SBAR (WHNP (WP What)) (S (VP (VBZ 's) (VP (VBN needed) (, ,) (PP (IN alongside) (NP (DT an) (NN evacuation) (NN plan))) (, ,))))) (VP (VBZ is) (NP (DT a) (JJ realistic) (NN program) (S (VP (TO to) (VP (VB stabilize) (NP (NNS conditions)) (PP (IN for) (NP (NP (DT those)) (VP (VBN left) (PRT (RP behind)))))))))) (. .)))
Those left behind will need a program for stabilizing conditions if they cannot evacuate. 
( ( Those left ) ( behind ( ( will ( ( ( need ( a program ) ) ( for ( stabilizing conditions ) ) ) ( if ( they ( ( can not ) evacuate ) ) ) ) ) . ) ) )
(ROOT (S (NP (DT Those) (NN left)) (ADVP (RB behind)) (VP (MD will) (VP (VB need) (NP (DT a) (NN program)) (PP (IN for) (NP (VBG stabilizing) (NNS conditions))) (SBAR (IN if) (S (NP (PRP they)) (VP (MD can) (RB not) (VP (VB evacuate))))))) (. .)))