1)
What is the meaning of "va'Yinachamu"?
1.
Rashi: They retracted to think if there is a way to salvage the remnant.
2.
Malbim: Until now, they thought about the past, if they suffered due to a transgression. Now they thought about the future. The Shechinah dwells only if there are 12 Shevatim. If one will be missing, it is a permanent blemish that cannot be fixed!
2)
Why did they say that the Shevet was cut off? There remained 600 men!
1.
Malbim: The next verse says, we cannot find wives for them. (The Shevet will cease when they die!)