What are the three possible outcomes of this secondary contact between the populations, and 2)?

We're missing some background information.  If you want a good answer here, you have to present the information and question exactly as these were presented to you.

There are more than three possible outcomes of contact.

1.  The two populations remain essentially separate while occupying the same area.  Imagine two bird populations that, during their long separation, now have different dialects of "calls" and "dances."  They do not choose to interbreed because the strangers are too weird.

2.  Extinction.  One population is more successful at resource grabbing than the other in the shared area, and the less successful becomes locally extinct.

3.  Fusion.  The two populations freely interbreed and are quickly one population.

4.  Hybrid zone formation.  The parental groups remain essentially distinct and don't occupy the same area.  The space between the two groups becomes populated with hybrids.  This arrangement can be maintained for generations.

5.  Reinforcement.  The hybrids are less capable of thriving than either of the parental groups.  This would tend to keep the parental groups from becoming one group.

6.  New species creation.  The hybrids are better at thriving than the parental groups, either using the same resources (in which case the parents go locally extinct e.g. California wild radish versus its parents jointed charlock and radish) or using different resources (in which case you now have three populations).

You can see that the hybrid fitness is dictating the outcomes of scenario

3:  Everyone is one big happy family

5.  The hybrids suck, and the parental groups remain distinct

6.  You now have one population of hybrids, or three populations.