Did all of Robb's army come to the wedding?
No. However, the grand majority did, meaning the events of the Red Wedding essentially ended the North's resistance.
The page linked above has a list of the location of all characters according to the book who were killed/captured at the Red Wedding. From the page:
Though no definitive count is known, most of the northmen are killed
while House Frey loses only approximately fifty men in the camps, as
well as Ser Garse Goodbrook and Ser Tytos Frey, both of whom are
killed by Sandor Clegane.
The list of absentees from the wedding reads as follows:
Perwyn, Olyvar and Alesander Frey are all noted as absent. It is
believed they were too sympathetic to Robb Stark and his comrades to
Lord Jason Mallister, Galbart Glover and Lady Maege
Mormont are sent to Greywater Watch with a force to find Lord Howland
Reed. They also carry a letter from King Robb naming his successor.
Lord Jason later returns to Seagard.
Ser Brynden Tully stays behind in
command at Riverrun to defend the Riverlands as Warden of the Southern
Marches, with the aid of the River Lords.
Now, the first two collections of people were never in Robb's army, but Brynden Tully is a notable absentee.
Also, when dealing with the aftermath:
The Red Wedding brings an end to the northern rebellion, with Roose
Bolton being made the Warden of the North for his aid in it, and
several great benefits befell House Frey, including the lordship of
Riverrun. However, it also destroys what honor is left in the house,
as they violated one of the oldest and most sacred traditions of old,
the guest right. This leads to antipathy and disgust towards the house
by most Westerosi, including their own allies. Additionally, though no
other house has dreamed to repeat the breaking of the right, it has
left a more lasting stain on the ancient guest right, with safety and
security in a strange castle no longer being considered guaranteed.
Since the Red Wedding, several of Lord Walder Frey's kin have been
killed by the Brotherhood Without Banners, northmen such as Wyman
Manderly or the "Ghost of Winterfell" in retaliation. Perhaps
ironically, more Freys have died due to the repercussions of the Red
Wedding than during the War of the Five Kings.
So although his army was defeated and his resistance destroyed, there were other Northmen and clans who survived and put up a resistance - but again, they weren't really a part of his army to begin with.
Interesting though, it's worth pointing out (especially since this is Movies & TV) that unlike the novels, in the TV Series Jon Umber is not present at the wedding. He was liberating the Riverlands during Season 2, but as per Bryan Cogman (one of the producers of the show):
well, keep watching! But he wasn't captured at the [Red Wedding] in our