It already is the language of business and also the scientific world. It has been chosen, for better or worse, as the lingua francua of the world and I don't see anything changing that.

I have friends in Germany, Austria and Hungary who are natives of those countries, and yet in their working day to day life they speak in English. When you have people of different nationalities, or a multinational company the language most likely to be shared is English.

But no your native language won't disappear, you still speak Dutch outside the office, right? And you like speaking Dutch I presume. There is no reason for or pressure for it to die out. I imagine if someone proposed making English the national language of the Netherlands people would object, probably very very strongly because the native language is a very important part of the cultural identity of your country, the same as it is for any country.

The case of Gaelic is completely different. Ireland was under the control of England for a part of its history, where of course the native language was English and the use of Gaelic was frowed upon by the English. This isn't going to happen any time soon with the Netherlands, and is increasingly unlikely to occur anywhere nowadays.

Gaelic also hasn't disappeared and its usage is on the rise within Ireland, where more and more people either speak it as a native language or are bilingual in Gaelic and English. 

I hope English doesn't completely take over. That would be boring. I like the different languages it shows the countries personality. If everyone speaks english then people would start becoming too similar and the other cultures my be lost or at least some aspects. It would be easier if everyone spoke English, but not as fun.