How is it possible to use a phase as a return path?
Figure 1. Voltage on red phase relative to purple phase. The lower set of arrows shows the resultant 'waveform' samples referenced to a straight X-axis.


  Now, does this mean that there wont be a return path at time 0.1? 


Have a closer look. The red and purple cross at 1/12 (not 1/10) which is 30° into the purple cycle.


  What will actually happen to the load at the instant where both phases are either in the positive half or negative half?


All that matters is where they are relative to each other.

Note also that the phase to phase voltage is 30° ahead of the red phase.







simulate this circuit &ndash; Schematic created using CircuitLab

Figure 2. The red-purple phasor (green) is 30° ahead of the red phasor.