If paper return filed, can i get acknowledgement from website in future if original acknowledgement lost.

No not on the website.

If you filed paper return, you will have to approach your Jurisdictional Income Tax Officer and request for a duplicate copy of your return acknowledgment.

no , NOT POSSIBLE .

if assessment is done u/s 143(1), then the order itself is sufficient, no need of aknowledgement 

Banks insist on acknowledgement of return for issuing loans. His ITO should be able to issue a duplicate.

Contact your Assessing offiicer