It depends, I think that in some situations it could be used, but it´s rarer these days indeed (I think it´s used certainly in more formal ways).
Anyway, in informal/colloquial settings you can use "dudes/buddies/guys" and other words instead of "folks".
"That´s all folks" would be understood because it´s a fixed expression.
On the other hand, don´t use "guys" with a group of people from the UK (message board, for example), the women of the group would take offense and state that they don´t like to be called "guys". At least if you are not long acquainted to the group. And even if you are, if the group is of a certain age bracket.
That is, when in doubt, be on the safe side.