No. A synchronous process will simply create a register. As such, there is no requirement for branches to be "complete". Be careful if you're relying on ordered assignments, though. For instance, the following:
signal1 = 1'b0;
case(condition_sig)
1'b0:
signal1 = 1'b1;
endcase
Some synthesizers (particularly if you have the synopsys_full and synopsys_parallel options on) will not do preemption and simply ignore the blocking statements if this is a clocked block. That is, it will treat the blocking assignment as non-blocking.
To avoid this, a rule of thumb is to always use non-blocking assignments in registered blocks.