If you were 100% cash right now which option would you pick over 10 years?

Invest it all into the indices or get a guaranteed 50% return on the income you invest after 10 years? This is the situation I'm in at the moment. My bank is offering gics at a rate at 4.15% per year if you lock in for 4 years or more through their GICs. I know alot of people say the indices are safe but looking back a few months, some people are already down 20-30% on their investment and further drawdown is expected.