AlysMS talked about using "the Boeings" for the foreseeable future. Most of those Boeings are 737s which could be replaced with C919s.
sure, but first C919 has to actually enter flight tests. including actually flying and Enter Production before you can Place the President of The PRC on it.
as for the Current 737s, a number have been modified to meet the PLA needs by the Chinese, Boeing does not support those airframes as the modifications were done by the PLA in violation of trade agreements, back in the year of our lord 2005,
( if you wish to see how it played out way back yonder click on the link to visit This Forum's great great granddaddy... It actually predates me!)
The PLA should have ready access to spare parts from retired 737-300 on hand as that model has been phased out with Chinese state owned airlines like China Xinhua Airlines retiring there 737-300's in 2011.
basically until Comacs are in production they cannot be used as VVIP types and even then a number of changes will likely be made that will add more time to deployment of those types, and those will only really be suited for domestic use. External use is likely to remain 747-400 those birds are in good shape and plentiful spare parts for the foreseeable. eventually they will be replaced like all things Air China who operates them for the State company also has 7 operational 747-8I that could do the job as well. so from a practical perspective there is no need to order any new planes just yet.