Buy another HPS lamp?

A question from a fellow grower:

I have 3 autos, noe in their 7th week since germination (one white dwarf, one critical and one skunk). For the first 5 weeks I used a 400 w MH lamp, and for the last 2 weeks I was using a 400 w HPS lamp. But 3 nights ago my HPS lamp broke down and I had to switch back to MH lamp.
Do you think I should buy another HPS lamp and go back to using it, or just stick with the MH lamp and finish the harvest with it?

you can get conversion bulbs which will get you a better light spectrum or finish whole grow with MH