The Vilnius-Warsaw train service is currently suspended.
Yep, first there was a bus substitution for the short cross-border leg, but now even that option is not available. Anyways, from the rumors it all connected with construction works (Rail Baltica line border-Kaunas)
What is the ticket trick for Warsaw-Prague?
For those who can't get discounted tickets (but still want to travel mainly by rail) there are a few tricks:
a) "easiest": in advance via CD eShop purchase ticket Bohumin-Prague (310 CZK, can be printed at home), while in Poland simply get Warsaw-Zebrzydowice domestic PKP ticket (since "Chopin" in Poland consider TLK it will be just 65 PLN) and international Zebrzydowice-Bohumin (8,2 EUR or 6,4 if same ticket purchased in Czech Republic). Such "combination" of three tickets instead of one international Warsaw-Prague allows to save some good money (roughly 35 euro vs. 81 euro when international ticket Warsaw-Prague bought in Poland or 55 euro when bought in Czech Republic)
b) "even cheaper": travel via Cieszyn/Cesky Tesin. Key idea here is that it's possible to omit paying for any international tickets, meaning that you get to Cieszyn using relatively cheap Polish domestic fares, cross the border by foot and then already use Czech domestic fare. Minuses of this route is that it takes longer & in most cases will involve short bus ride (Cieszyn isn't all the time reachable easily just by rail)
c) "interesting": also possible to travel from Warsaw to Prague via Wroclaw/Jelena Gora. Also as in a previous case such route will be longer than using direct train. Regarding tickets trick is the same as above - domestic PKP fare till the border, short cross-border fare (either Meidzylesie-Lickkov or buses via Nachod/Harrachov)