You should keep AS for status for now. DL will have full reciprocity soon. AS miles are easier to use than DL
You can get to Plat on CO by match. Use that status for UA travel. 20k in C = 30k in MQMs more than enough to stay 2p next year (good for occasional domestic Y in e+)
India is served by CO via EWR. From there to SIN and SYD is by SQ and then you can keep NZ or UA for trip back.