I can’t fathom the concept of putting sealant in a quality tubular on a prophylactic basis. Furthermore, other people must have better luck repairing tubular punctures with sealant than have I. For a glass shard type puncture, I have never had sealant hold above about50 psi…So, in theory, you could sag home but not much more. I can’t imagine relying on a bottle of sealant as one’s roadside repair kit. I have had some luck sealing slow leaks with sealant…the type of leak that is caused by Michelin wire, etc. There is one big caveat….Once a tire has had sealant, the sand is running out of the hourglass for that tire for the last time. If you let that tire deflate, there is an excellent chance that the inside surfaces of the tube will bond to one another…and, of course, the sealant sealing the puncture has a finite life and may have to be augmented. You can get a little more use out of the tire, though if those obstacles are avoided. I carry a spare…a tire that has been used and has glue residue on the basetape. It will form a contact bond with the residual glue on the rim if a roadside change is necessary and after ten minutes or so of riding, the bond will be pretty effective. I know some people buy cheap tubulars for use as a spare, but I always have some used good tires that are worn and have been retired from primary use. A good tire folds so much smaller and is infinitely easier to to mount at roadside.