Can I take leaves on loss of pay while in H1B ?

No "benching" of any kind is allowed while on H-1B status. You could be deemed to have "fallen out of status" without you or your employer realizing it, until it's too late. Speak with the employer's immigration attorney(s), but avoid broaching this subject or anything at all with the "HR' department or any "immigration team" who are not licensed lawyers and who will not know what the laws in this regard are.

You should be fine to travel without pay