Converting 3×7 speed into a 2(chainrings)×1(sprockect) I own Firefox Rapide 21s, which has Acera 7s(14-28t) groupset are rear and Tourney 3s(28-38-48t) groupset at front.

In a recent accident, the rear derailleur took some impact and is bent now, it doesn't latch on to 7th &amp;1st gear. I went to a mechanic he applied some pressure to make it straight, he said it(method) could potentially make the derailleur straight, and I don't want to spend money in getting a new one.

While coming back home, I tried to shift up to 1st gear to see what happens -- it dug into one of the spokes, locking the tyre, making me fall. Now that spoke is bent and has become loose.

However, the real question is:
Now, I don't like the method he has proposed to straighten it. Hence, I have decided to remove all the gears and make it a single speed.
My focus always has been higher speed, so I'm thinking of getting 53t×11t(chainring×sprocket).
But I'm also thinking - the ratio that setup makes might be a little bit too much for me in all circumstances.
Therefore, I was thinking of fitting a double crankset up front(possibly 34-50t or 39-53t) and single sprocket(possibly 12t or 14t, respectively).
Or is that even possible?

I goolged and looked at most places, but could find any answer.
Without a rear derailleur one cannot switch gear on the front chainring. The length of the chain would differ between chain rings. The derailleur compensates this by running the chain a longer path that may be shortened by moving the derailleur arm. It also tensions the chain due to its spring, which hold the chain on the chainring.