I dislike a competition where undefeated teams get eliminated.
While it is possible, it isn't exactly likely, and given the low amount of ties in this World Cup, it's very unlikely that this will happen.
My brother told me it happened in a previous World Cup. It shakes my faith in the design of the game and tournament in general, even if it isn't likely this time around
That's... a little weird. When it happens, it's because other teams did poorly. Here's the most recent example (in 2010) :
Group F of the World Cup (Paraguay, Slovak Republic, New Zealand, Italy) :
Italie and Paraguay tie (1-1)
New Zealand and Slovak Republic tie (1-1)
Paraguay beats Slovak Republic (2-0)
Italy and New Zealand tie (1-1)
Slovak Republic beats Italy (3-2)
Paraguay and New Zealand tie (0-0)
Paraguay has 5 points (Win/Tie/Tie), Slovak Republic has 4 points (Win/Tie/Loss), New Zealand has 3 points (Tie/Tie/Tie), Italy has 2 points (Tie/Tie/Loss). Paraguay and Slovak Republic advance, New Zealand is out without losing a game.
To avoid this situation, you'd have to go back to the old scoring system (it changed with the '94 World Cup I believe) where a win was a only worth 2 points. The reason this was changed to wins being worth 3 points is to rewarding actually scoring goals and make ties less appealing, which forces teams to actually go out there and try to score. I don't think there's any problem with New Zealand being eliminated there : sure, they didn't lose a game, but they didn't win one either.
I'm sure there's an example where a team goes Win/Tie/Tie and still doesn't make it because of the tiebreaker, but again, it would be a case of rewarding the more offensive team, which is good for the game.
PPE : I don't know why Portugal would be likely to beat Ghana. I would bet on a tie, and based on how Ghana played against Germany, I'd say a Ghana win is more likely than a Portugal one.