AFAIK, openbazaar.org itself is build with the use of IPFS protocol which is projected to be the base of Web 3.0.
Doesn't IPFS only use IPFS to store the content of the store (e.g. list of items with it's price/description), which is useful when the merchant is offline ?
IPFS network and CIDs it holds are accessible 24x7 no matter if merchants are online or offline. Their frontend web servers connect to that content via available gateways chosen when merchants' sites where build.