The tube does need to repaired correctly, a repair facility may be able to "extract" the remaining tube, similar to extracting a broken bolt. You may plug it for now, there will be no high pressure, but there will be splashing of oil and whatever material you choose to plug this hole will have to be resistant to constant hot oil against it. I would consider this a temporary method until you can decide on what to do. If the plug does come off while you are driving you may not realize until most of the oil seeps out, and could damage the motor. If the only method seems to be removing the oil pan, you may want to consider "tapping" the hole with a similar sized bolt, and thread it in, this may be more permanent as far as no oil escaping. Or you may want to grind the edges of the broken bottom of the tube and fit it in the hole.

-Rip