The point is that NIST contends that the damage sustained from the North Tower 'collapse' did not cause or contribute to the 'collapse' of WTC 7. Therefore debunkers cannot claim that WTC 7 'collapsed' due to a 'gash' without disagreeing with the official investigation they defend.

"Other than initiating the fires in WTC 7, the damage from the debris from WTC 1 had little effect on initiating the collapse of WTC 7." NCSTAR 1A, p xxxii

NIST, instead, contends that WTC 7 'collapsed' due to the new phenomenon of 'thermal expansion':

"Fire-induced thermal expansion of the floor system surrounding Column 79 led to the collapse of Floor 13, which triggered a cascade of floor failures. In this case, the floor beams on the east side of the building expanded enough that they pushed the girder connecting Columns 79 and 44 to the west on the 13th floor."

"The displaced girder and other local fire-induced damage caused Floor 13 to collapse, beginning a cascade of floor failures down to the 5th floor ... This left Column 79 with insufficient lateral support in the east-west direction. The column buckled eastward, becoming the initial local failure for collapse initiation." NCSTAR 1-A, p 19-20

Source: The NIST WTC 7 Report: Bush Science reaches its peak

Edit:

Furthermore, had the 'gash' really initiated the 'collapse', World Trade Center 7 would have dramatically toppled towards the South. Instead, it symmetrically imploded into its own footprint, exhibiting free fall acceleration for approximately 2.3 seconds at the beginning, indicating all supporting columns in the bottom floor had been removed simultaneously and instantaneously. Witnesses heard a countdown and a loud explosion. Several firefighters had already been informed since about noon that the building was either going to 'come down' or be 'brought down'. This better explains Silverstein's comment, in my opinion. We have expert corroboration from Danny Jowenko, a Dutch/European controlled demolition specialist, who is absolutely certain that WTC 7 was professionally demolished. He later reconfirmed this in a phone conversation with a 9/11 researcher.

He does not think, however, that WTC 1 & 2 were professionally demolished, but this is mainly because these buildings were destroyed in a totally different manner from WTC 7, namely top-down using an overdose of explosives; this is abnormal, but could have not been done differently considering the need for consistency with a collapse initiated from the damage at the upper floors. Reviewing the video evidence reveals that the perpetrators nevertheless failed miserably at making the collapse look 'natural'. Lastly, many severe anomalies in the steel & dust remnants from the rubble of all three 'collapsed' WTC buildings have been discovered, most of which have been described in the papers at the Journal Of Nine-Eleven Studies.

Most of the information I've just summarized for you is also available via Architects & Engineers for 9/11 Truth.

Edit 2:
I realize you may know all this already, but what I'm trying to say is that it has already been established, even in the official version of events, that the South side damage did not cause 'collapse' initiation for building seven.

In addition to SnowCrash's excellent reply, note that Mr. Long does state partway through the interview that he did not see any damage to WTC7 that would cause him to believe that it had been in any danger of collapse.