You can withdraw money from your Vantik account at any time, so it may happen that, at the time of your withdrawal, there will be less money in the Vantik account than you originally deposited. This is due to the nature of mutual funds, especially in the early years of your deposits. The value of your money may fluctuate - that's perfectly normal. Don’t forget that the Vantik Security Buffer will additionally protect your savings for your retirement.
If you've saved a few years, it's very likely you'll be making a profit. These profits are yours. In the event of a payout, however, these have to be taxed. Your deposits are never taxed.