They will have to fight for the second position. The second position makes it to the champions league play-off and since every team wants to be in the biggest competition in Europe, they'll fight hard for it.
Game week 30 might be the decider because that's when PSV and Ajax will face off. I feel the winner of that match might hold on to the second position and I have a feeling it would be Ajax.
I think the same, second place in the Eredivisie means a lot, second place means Champions League play-offs and if you go further it's a lot of millions, I don't know exactly but what international starting place does the cup winner get?
Feyenoord are in a good position in the Europa League, 1-0 is not a big advantage, but promotion is definitely possible.